Tight restrictions are enforced around the pier with no picture taking in the area, US Army watching for any violators, arresting them on the spot. The Panama Canal Zone is a military reservation. A man seen taking pictures jumps from a pier when discovered by military police. A pier full of passengers awaiting their sea plane to Panama City, first stop Balboa, are assembled, greeting one another after shortly debarking a cruise ship to the Panama Canal entrance. There are a few locals with the tourist travelers, who are also to be sea plane passengers. One traveler is a Czechoslovakian, estranged from her country after an invasion and political upheaval.
Mr. Godley offers Miss Finch one of his cigarettes, she enjoys smoking it before boarding the sea plane. Manolo informs employee Kathi Lenesch about a good-looking young American on the plane named Cabot, suggesting she get acquainted, find out all you can about him. Manolo welcomes Achmed Halide once on board the plane; Dr. Rudolph Grosser, beard, carries on a piece of luggage resembling a bird-cage shaped like a house, ignoring and defying the stewardess' instructions. Fasten your safety belts please, we are taking off, directs the stewardess or the sea plane attendant. She instructs Mr. Godley that smoking is not allowed as he attempts to secure his cigarettes before she takes his coat. Novelist Cliveden Compton sees their ship going the through the first lock of the Canal, informing those around him to have a look. When Kathi moves over to have a look at the ship, Dr. Rudolph Grosser stares at her while she watches the ship. She shows signs of uneasiness, looking back at him. His staring was obviously a signal of disapproval, maybe for her being on the plane altogether.
The plane lands in Balboa, visible merchants abound in the streets, including the hat purveyor, Fu Yuen, where Godley pays his cab driver in front of the panama hat shop. Godley greets tobacconist and passenger Achmed Halide, promising to visit his shop after looking to buy a panama hat at Fu Yuen's shop. Greeting the proprietor, Godley mentions I hear you are a man of many friends, and the owner replies, a thousand friends too few. You have enemies? One enemy one too many, responds owner, Fu Yuen. Godley then opens with I guess we understand each other Mr. Chan. Charlie says he prefers Fu Yuen when addressing him, to keep his identity a secret. While Godley tries on a hat, Charlie greets Achmed Halide standing outside the entryway, striking a match for his cigarette, obviously eavesdropping. Charlie tells Godley, in Panama the walls are equipped with eyes as well as ears, as they both note the suspicious behavior. Godley passes on information from Washington, the straight tip is there might be an attempt at sabotage when the fleet passes through the Canal. Charlie is responsible for the tip and he is also aware of the increased number of secret agents after the fleet was ordered back to the Pacific. The cloth worker in the hat shop front is shown eavesdropping on their conversation.
Godley tells Charlie, the person sabotaging the Eldridge drydock and crashing the 409 was a secret agent named Reiner, Chan agreeing, stating also, he is the one man we cannot spot. Godley describes Reiner as uncanny, a cold-blooded killer, and we think he is here in Panama. Charlie hopes Godley brings some slight clue to Reiner's identity, as he strikes a match for Godley's cigarette. Godley takes one puff, has trouble catching his breath, and before he could say anything more, he falls to the hat shop floor. Charlie searches his pockets for some identity papers, pulling out a cigarette pack, smelling the doctored contents, he pockets the cigs. Reaching for his flight ticket envelope, he eyes R.J. Godley written on it. Chan explains to police why he merely looked in the deceased-pocket was seeking identification. Achmed enters the shop, identifying Godley from the plane, describing him as well and strong when he left the seaplane pier. Sergeant Montero, the attending policeman, reaches into the other pocket pulling out Godley's diplomatic passport, accusing Charlie of being a spy, and taking him to headquarters.
Temporarily behind bars, Chan witnesses a crap game among the other cellmates, and recognizing the bottom which has received several spankings, his son Jimmy is swatted by his father. Jimmy was arrested taking pictures, while ashore, working as a steward on shipboard, during his college vacation. Jimmy reconciles with Charlie, from which he cautions Jimmy not to give away his identity. Captain Lewis escorts Charlie from the jail, after Sergeant Montero shows him the man he caught. Lewis recognizes Chan, stating he will take this man to the governor's at once; they leave Jimmy behind.
The glass door has the words Office of the Governor, Colonel D. C. Webster, stenciled on it and Charlie, Captain Lewis and the Colonel all discuss Reiner being in Panama. Charlie explains Godfrey was about to disclose something about the man when he dropped dead from the drug in the cigarette. Dr. Fredericks delivers the autopsy report on Godley, concentrated poison in both lungs. Chan names the poison, known to be most deadly when inhaled with smoke from a cigarette. Chan continues speaking about Reiner's signature crime included poison in the tobacco. Charlie stipulates, Godley and Reiner played a cat and mouse game; the mouse struck first. The fleet is scheduled to go through the Canal in the next 48 hours, per Colonel Webster. Charlie wishes to be Fu Yuen while they work on the case.
At the hotel, Jimmy is in the tub getting rid of the jail odors, while Charlie looks at the plane passenger list and seating assignments. Chan says Captain Lewis questioned the stewardess and all passengers; Jimmy says the murderer might have been on the plane; Charlie concurs. Chan shares with Jimmy, before boarding plane, Godley and the schoolteacher smoke cigarettes from his pack. Someone had to swap the deadly cigarettes in Mr. Godley's coat once on the plane, because he offered one to Miss Jennie Finch and he smoked one himself, before they boarded. Someone substituted poison cigarettes after boarding plane. Coat was placed on the rear seat by the stewardess, easily accessible by all passengers, per Charlie. Jimmy guesses one of the passengers is Reiner; Charlie responds, quite possible. Chan ponders what name could Reiner be hiding behind, as he goes through the list. Jimmy runs through the list as well, providing his opinions on each, saying Cabot is all but cleared, because he is a government engineer. Charlie gives a rolling eye look at his son for that comment. Dr. Rudolph Grosser is known to Charlie as a Viennese scientist, living over Achmed Halide's tobacco shop. Jimmy knows Grosser from biology class, an expert in tropical diseases and plagues. Chan sends Jimmy to investigate the doctor while he attends the cabaret to see entertainer Kathi Lenesch.
Dr. Rudolph Grosser walks down the street from the Hotel San Miguel, Achmed Halide lights his cigarette, ducking out of the line of Grosser's path. He juts out to stop Grosser, demanding he stop what he is doing. Grosser snaps back, the place he rents is big enough for him to do what he pleases. Achmed threatens he stop, but Grosses strongly advises him against it, all while Jimmy observes the two in the street before Grosser leaves. Compton happens along, Achmed invites him into his shop, to purchase more of his favorite mixture of tobacco; Jimmy watches them from outside the shop window. Halide recommends a new mixture for Compton to try, although it is more expensive. If he likes it, he will purchase it, drop it off at my hotel this evening, requests Compton. They part company, Compton pauses, noticing Dr. Grosser has his name plate on the inside of the shop, his office is upstairs; Jimmy watches intently as these two-part ways. Grosser descends the stairs, walking down the street, as Achmed closes his shop, dousing the lights. He lurks away from his place of business, as Jimmy carefully enters the stairs to Grosser's room, entering with his flashlight in hand. Jimmy is surprised entering the laboratory with a monkey screeching and showing itself. He views cages of creatures the doctor uses for his experiments, eyeballing a collection of rats with bubonic plague. The monkey jumps on Jimmy's back, as he makes a hasty retreat from the laboratory, without the monkey.
The music is playing at Manolo's cabaret, Kathi Lenesch entertains everyone with her singing, as Charlie watches her from a nearby table. Seated at another table is Richard Cabot, also listening to the lovely singer. Manolo stands aside, enjoying her singing, with the room filled with sailors. Compton is seated on the mezzanine, he gets up, enters the hostesses only dressing room. He opens a small suitcase, finding a foreign identification belonging to Kathi von Czardas, it has a picture of Kathi draped with a number badge on a string. He puts the foreign identity badge in his coat pocket. Charlie pays his respects to Manolo at the bar by saying for the many times you visited my store, I am now returning the complement. He tells Manolo, death visited his humble shop today. Manolo acknowledges knowing of the passing of Mr. Godley in the hat shop. A sailor tells an MP the singer Kathi is asking about the fleet passing through the Canal; the whole issue is put to rest by Manolo explaining the economy of the entire area is dependent upon the fleet coming. She is escorted off by Richard Cabot, as Charlie observes the entire incident, and the couple depart for the upper level. She tells Cabot if he really wants to help her, don't ask any more questions. Sergeant Montero escorts Miss Jennie Finch into the club, Manolo greets her, walking them to a table. Jimmy invites his father to join him elsewhere to see what he has seen, when Montero recognizes the detective as the man he arrested earlier. He busted out of jail? Charlie returns with no reason to bust, I walked out. Manolo inquires why you were in jail? Montero tells Manolo why he arrested Fu Yuen earlier, then Miss Finch comments, oh another spy? The entire bar of mostly sailors turns toward the comment heard. Montero scolds Miss Finch for nearly starting a riot by saying the word spy. Jimmy speaks out, he is Charlie Chan; now everybody around knows who he is. Chan excuses himself to Manolo, requesting a rain check on the hospitality offer, stepping outside the club.
Jimmy confides in Charlie what he saw in Dr. Grosser's laboratory. Chan visits the lab with Jimmy after hearing about the experimental rats caged and labeled bubonic plague. They both enter cautiously, Achmed is hiding behind a partition, Jimmy notices a light on, fears the black cat in the lab, hears a noise, Achmed leaves unseen with a satchel, the two Chan's look about the laboratory. The rodents are gone from their cages, as Charlie casts doubt upon Jimmy's imagination. Jimmy insists the cages they are standing in front of were full of rats when he was there earlier, and somebody left the lights on. Charlie calls Governor Webster, requesting Dr. Grosser be picked up for questioning. Webster follows through with the order on Grosser and has an alert to the Medical Corps for a plague warning. Webster queries if there was anything else, when Charlie picks a business card from Grosser's desk. It is Compton's business card, which had the words written upon it, please call me at the Hotel San Pablo. Chan also requests, from British consul, a complete background check on Cliveden Compton, English novelist. Charlie walks across the street to his hat shop and residence, locking Jimmy inside and saying goodnight; he has small errand to run, do not wait up.
Charlie enters the Hotel San Pablo foyer, spots Achmed at a table, Halide notices Chan pass nearby heading to the front desk requesting Mr. Compton. The desk clerk says the key is still here, the guest must be out. Charlie responds, I will wait. Charlie sits at a table adjacent to Achmed, requests coffee, Achmed departs, as Sergeant Montero is escorting Miss Finch into the foyer; she is suspicious of Achmed, informing the Sergeant. Montero instructs Finch, if you don't stop playing detective, somebody is going to kill you. He says good bye to Miss Finch, Charlie watches, while Kathi is out front, telling Manolo she cannot continue with her job, based on what happened tonight. Manolo commands her to return to work, after stating clearly, she is very independent for someone without a passport. Manolo watches Chan leave his table. Charlie heads upstairs, while the desk clerk is distracted with a phone call. He knocks on the door, a masked man is inside, hears the knock, slides under the bed, as Charlie enters the dark hotel room. He notices movement from under the bed, that person tries to escape, Chan covers him with a blanket. It is Jimmy, nosing around the room, when he should be in bed.
Jimmy informs Charlie that Compton is an Englishman, possibly Reiner posing as such, even his humidor has an English school emblem. Jimmy makes mention how sentimental Englishmen can be of their schools. Do you suppose an operator as clever as Reiner would be ignorant of same? Chan remarks. A pistol through the veranda doors appears, aimed at Charlie, as he looks around the room. Eyeing the weapon, Jimmy throws the humidor at the weapon, dislodging it from the intruder. Charlie grabs the gun off the floor, pursues the uninvited onto the veranda, but nobody suspicious is seen. Chan eyes the shattered vessel of tobacco, he picks up an identification book out of the container. It contained Kathi's foreign identification, stolen earlier by Compton from the club dressing room. Charlie explains to Jimmy some European countries use these to keep police records of all citizens. There was also a hand-drawn map with the ID, and Charlie tells Jimmy, here is another item providing reason I would like to talk to Mr. Compton. Jimmy claims it is a military map. Charlie says the map is a drawing of the old Panama cemetery, rolling his eyes at his son.
A sound at the door makes the two move out of sight. Kathi enters the room asking for Mr. Compton, as she begins a search, Charlie steps out, requesting the reason for her search, possibly the stolen identification. Kathi said Compton telephoned her tonight, saying he had the ID. He would return it if she answered a few inquiries. Chan indicates maybe Compton knew Baroness von Czardas might be a secret agent, adding, truth would win more friendship than lies. Certainly, Compton suspected me, she reveals to Chan, so she concealed her identity, because she was afraid of being sent back. Chan replies, the map of Europe has lost your native country. I could be sent back, I have no passport. Please don't give me away, I want to make a new home in the United States. My father and brother were executed because they spoke of the cruelty of the invaders. If I return, it would mean death for me or the concentration camp. Charlie interrogates if she knows a person named Reiner. Kathi responds, Reiner was a member of the secret police who arrested my father and brother. Chan explains, on soil of democracy, you are safe from persecution. She requests her identity card, Charlie responds, later, adding, inside my pocket is like the vault of the national bank. She receives assurance Charlie Chan will not share the information with anyone, requesting permission to return to work. Charlie and Jimmy resume searching for anything else Compton might have possessed. Jimmy opens a closet door, out falls Compton, dead. Charlie checks his papers, they confirm he is Cliveden Compton. He was shot, confirmed by Chan's comment to Jimmy, no heart strong enough to hold bullet. Jimmy speculates the man could have been Reiner, killed by the Baroness. Charlie directs Jimmy to call police, but the phone wire has been cut. They exit, Manolo is coming home, they use his phone to notify the police of Compton's death. Chan calls military police while Jimmy offers Manolo one of his cigarettes. Charlie talks to Captain Lewis, reporting Mr. Compton's death at San Pablo Hotel, stating emphatically, Compton murdered. Charlie demands to know where Jimmy got the cigarettes. He claims they were on the table in your room. Chan says they are cigarettes from Mr. Godley's body. Manolo panics about inhaling the cigarette. Charlie demands to know how Manolo knew the poisoned-cigarette secret shared only by police and murderer? Manolo responds by knocking over the desk lamp, pushing Chan away, running out of the room, leaping from the balcony to the street, and disappearing. Jimmy is on the bed thinking he is a goner, moaning, when Charlie tells him cigarette quite harmless, they were not Godley's, you will be okay. Jimmy again speculates Manolo could be Reiner.
Gun can be made to talk according to Charlie, as the ballistic evidence has the same gun fired at Compton and pointed at Chan. He shows Colonel Webster and Captain Lewis the gun. Webster adamantly confirms the test bullet matches the murder bullet. Marks left on gun barrel like fingerprints, Charlie adds. Webster learns the same gun he has in hand is registered under Manolo's name. Lewis asserts, the police have been on the lookout for Manolo ever since he ducked out of the hotel last night. Charlie says Manolo could be Reiner or a confederate. Where does that puts Compton in all this? Why was he killed? Charlie asserts, we will know more when the identity of Mr. Compton is established. Colonel Webster states Manolo could be Reiner, so could the missing Dr. Grosser. Webster tells Charlie, the Fleet goes through the Canal today, we have got to break this, you have got to get Reiner. Chan promises his humble best.
Charlie and the Captain enter under the Santa Carmen cemetery gate, Achmed is behind them, watching their entry onto the grounds. Captain Lewis refers to the map, X marks the spot, but where is the spot? Achmed observes two men pause to get their bearings. Miss Finch runs up to the men screeching, there is someone alive in one of these tombs, come quickly. Finch asserts she was there photographing the stain-glass windows on one of the older tombs, when she heard a groan. The name on the tomb reads Achmed Halide. Achmed watches the group from a distance, Charlie enters first, gun drawn. The sounds are coming from Jimmy, tied up and gaged. Jimmy explains to his rescuers, while Halide listens outside the tomb. Jimmy attempts his best explanation of the recent events, showing everyone where he was standing when struck from behind. He never got a good look at his attacker. Leaning on a wall, it suddenly opens, giving way to the lower level tomb, which Jimmy falls down the stairs. Charlie pushes the blocks open to view the tomb cellar. All group members survey the lower tomb contents. Finch shows Chan an assortment of articles necessary for disguise, namely a mirror and makeup pencil. Captain Lewis opens a trunk containing empty tins. Lewis directs Finch and Jimmy upstairs. Chan observes the trunk designed to treat its content gently. Jimmy grabs an empty tin, Lewis grabs a full one, while Chan takes a taste of the contents from Lewis' container. Chan declares it was explosive in the trunk, he adds some of the cans were emptied recently to other containers. The four go upstairs, ready to leave, Finch finds the tomb door locked from the inside.
A suspicious-looking bottled-water transport driver pulls up to the closed gate of the Power Control Miraflores Locks, a military attendant checks his Pass-ID, it is a piece of paper signed by D.C. Webster. The driver is seen carrying the jug of water into the hold of the Powerhouse, placing it atop of some lockers with wrapped packages he places next to the jug. The packages are drinking cups for the water, but he opens one of them revealing a triggering device for explosive. His appearance is a local, big moustache, hat and dirty shirt. He sets the timer on the device, an officer requests for and receives a cup from the driver, just before he puts the detonator behind the jug. The Colonel is in his office, concerned when there is no word from Lewis, no word from Chan, either.
In the locked tomb, escape ideas are impractical, with Finch suggesting they get out by detonating a small amount of the found nitroglycerine. Chan rejects the idea, too dangerous. He hears someone outside, a man approaches, opens the door, Lewis orders him to put up his hands, he strikes Lewis with his flashlight, and runs away, with the three men in pursuit. Jimmy spots the man running, two shots are fired, the man goes down. Neither Chan or Lewis fired a shot. Left behind, Finch claims someone fired two shots and ran past her. Charlie examines the downed man, peeling his fake moustache away to show it is Manolo, dead. Finch claims that is the third passenger to die. Charlie pulls the Powerhouse Pass from Manolo's pocket, proving he was the driver. Chan says we must find a telephone at once. Charlie calls, implores Webster to make immediate search of Miraflores Powerhouse for explosives. Webster calls the plant; the detonator clock is pictured, as Dr. Grosser enters the office while the Governor is on the phone.
Lewis with other officers agree their hope is to find where Reiner planted the explosives. The passengers claim soldiers were sent to bring them to the Powerhouse. The Governor shows, ordering immediate evacuation of building. Lewis, fellow officers, and another personnel leave. Charlie holds his gun in his coat pocket requiring the five remaining passengers be detained. Moments ago, Mr. Cabot strongly doubted existence of a bomb, now he protests being held with the other passengers. Chan lectures the group with you are all suspects in plot to sabotage fleet. One among you is the notorious master of sabotage known as Reiner. Only Reiner knows where nitroglycerine is hidden. Only Reiner knows when bomb is set to explode; only Reiner can save own life and your life. Chan continues, can he wait minute by minute, second perhaps by second, knowing exact moment explosion will send him to join his ancestors.
Achmed accuses Grosser of being Reiner, bringing in his laboratory rats to set a plague upon the population. Dr. Grosser admits to bringing the rats in illegally for experimentation, but when he found all the rats were stolen, he did not hesitate to report to the Governor in person. Grosser is accusing Achmed of stealing the rats, Achmed says of course he stole them. Charlie wonders why Achmed with his frequent trips to the cemetery. He explains to Charlie he bought the crypt years ago as a final resting place, but recently he learned others had visited there and it is used to hide something. Achmed suspected Dr. Grosser of being Reiner. Chan quizzes, how come you know Reiner? Achmed explains Compton was a member of the British Secret Service on the trail of Reiner and I sold him information, for which I learned the name of Reiner. Ached becomes incensed with Chan holding the gun, pleading to get out of the plant. Chan pulls the gun from his front coat pocket. The others are insistent of leaving and talk about rushing the detective, three against one, implies Grosser, even though he has a gun. The men move toward Chan, Charlie demands they stay where they are, as Miss Finch pulls a gun from her purse, ordering Charlie to drop the gun; he complies. She moves toward a closed door, opens it and is greeted by Captain Lewis, another officer and others, including the Governor and Jimmy. Captain Lewis takes her gun. Finch threatens Chan he will die with her.
He says correction, Miss Reiner, sorry to steal moment of triumph, but time bomb without electric arteries cannot speak. Infernal machine rendered harmless before the arrival of suspects. To the rest of you, the trick was necessary to force Reiner to betray identity through fear of death. Miss Reiner your reputation for cleverness not exaggerated. Our timely arrival in cemetery today prevented cold-blooded murder of favorite son. Knowing Captain Lewis and I were about to find Jimmy, she cleverly leads us to him, at same time she was planning to lock us in tomb. She locked herself in the tomb with the rest of us, knowing the explosives were already on their way to the Canal; explosives were removed prior to our arrival. This gave her the unbreakable alibi she needed when the man came to the tomb. When she gave an alternative to escaping using nitroglycerine, but the nitro was never revealed by Chan, she overplayed her hand, giving herself away as saboteur. Charlie takes her gun from Lewis, to demonstrate too late to punish your confederate Manolo for the murder of Compton and Godley, however, ballistic science will prevail that bullets fired from your gun, killed Manolo in the graveyard tonight. Take her away, directs Chan to Lewis. Chan then addresses Kathi as Baroness, betrayer of loved ones will now receive just punishment, as the music begins. The detective, his son and other innocent passengers are accompanied with naval personnel viewing the Fleet move through the Canal.