On New Year's Eve 1974 in Los Angeles, California, Monk Riley (Julius Harris), the editor of Glance Magazine, is unable to locate Shawn North, his favorite photographer, so he telephones Shawn's assistant, Friday Foster (Pam Grier), a young African American woman. Monk orders her to the airport to photograph the arrival of Blake Tarr (Thalmus Rasulala), known as "America's wealthiest black millionaire", who has been out of the country for years. Before she can leave her apartment, Friday receives a telephone call from Clorils Boston (Rosalind Miles), her best friend and a famous model, who begs Friday to come to her party. Although Clorils claims it is a matter of life and death, Friday explains she has to work.
At the airport, Friday bribes a guard to get access to Tarr's private hangar. As she hides and readies her camera, three assassins, Yarbro (Carl Weathers), Chet Freed (Tony Brubaker), and another man, enter carrying automatic pistols and dressed as security guards. As Tarr and his entourage enter the hangar, the three assailants shoot him in the shoulder and kill most of his bodyguards before the police arrive. As Friday photographs the gun battle, Chet is wounded and escapes by a side door while Yarbro bumps into Friday as he runs away. Yarbro leaps into his car, and a car chase ensues during which a police cruiser crashes into a truck. A bleeding Chet arrives at Clorils's home and drops dead at her feet.
Later that night, Riley bawls out Friday for almost getting killed, but changes his tune when Shawn North (Stan Stratton) arrives and they develop the film. One of Friday's photographs shows Chet's face. Friday has seen him before, but cannot remember where.
Note: a minor unrelated subplot involves Friday's younger teenage brother Cleve (Tierre Turner) who lives with her and does some black market dealing on the sides with a local pimp named Fancy Dexter (Ted Lange) for some valuable items to earn some extra spending money.
The next day, Clorils is backstage at a fashion show talking on the telephone, begging "Charlie" to help her. When Friday arrives, she goes to assist Shawn, but runs into Colt Hawkins (Yaphet Kotto), an old friend and private detective. Their reunion is interrupted when Madame Rena (Eartha Kitt) steps onstage and starts the fashion show. As models parade Rena's wares, Clorils stumbles from behind the curtain with a knife in her back. With her last dying breath, she declares that she wanted to save Chet from "Black Widow." When police lieutenant Jake Wayne (Edmund Cambridge) arrives, Madame Rena tells him she believes that Ford Malotte (Godfrey Cambridge), a rival designer, killed Clorils and reveals that Malotte has been flying Clorils back and forth between Los Angeles and Washington, D.C. for months.
Later, Friday is in the shower at her apartment when Yarbro sneaks into her apartment carrying a switchblade knife. The telephone rings, and Friday goes to the living room. She sees Yarbro and runs into the hallway... clad in only a towel. A neighbor appears, and Yarbro flees. After Friday reports the attack to Colt Hawkins and Lt. Wayne, she learns that Chet's body and a cache of narcotics were found in Cloril's house. Friday realizes it was Chet she recognized in her photographs.
A few days later, Friday spots Yarbro at Clorils' funeral, but before she can react, Yarbro gets in his car and drives off. Friday leaps into a nearby hearse and chases him to an abandoned warehouse, where Yarbro tries to strangle her. Friday douses him with pepper spray and runs. Two policemen appear and arrest her for trespassing, allowing Yarbro to escape.
Later, at the Glance magazine office, Colt Hawkins informs Friday and Riley that Ford Malotte arranged meetings between Clorils and U. S. Senator David Lee Hart (Paul Benjamin) in Washington D.C. Shawn arrives with more photographs of the airport gunfight and Friday recognizes Yarbro as the man who tried to kill her.
The next day, Friday and Colt fly to Washington and meet Malotte at a bar catering to a homosexual clientele. Malotte clams up when Friday mentions "Black Widow." Thinking Colt's manly charms might persuade him to talk, Friday steps outside. A red Ford Mustang screeches around the corner and chases her down an alley before crashing into a power line and electrocuting the driver. Later, Malotte telephones Blake to inform him that Friday knows about "Operation Black Widow." As he talks, Yarbro arrives in a truck and smashes into the phone booth, crushing Malotte.
Across town, Friday crashes Senator Hart's fund raising party and meets Rev. Noble Franklin (Scatman Crothers), a lecherous old preacher who invites her to his estate, "Jericho," to give her a "private interview." The Senator interrupts them and when Friday tells him she is a friend of Clorils, he suggests they go back to his place. Before they leave, however, the Senator tells his assistant, Charles "Charlie" Foley (Jason Bernard), to handle the party guests.
At the senator's home, Hart tells Friday that his people believe Blake Tarr staged his own assassination attempt as part of an operation called "Black Widow." However, they have not been able to discern what "Black Widow" is. After a few drinks, Friday and Hart make love.
The next morning, Charlie meets Enos Griffin (Jim Backus), a wheelchair-bound millionaire at his estate somewhere in Virginia who is funding Hart's political career. Charlie tells Enos he believes he can use Friday to flush out Blake Tarr.
Back in Los Angeles, Madame Rena orders Friday to meet her at her office. When Friday and Colt arrive, Yarbro appears and shoots Rena. Colt gives chase while the dying Rena gives Friday a telephone number. Colt chases Yarbro down across the streets and rooftops of various buildings where he catches up and kills him in a gunfight. Without informing Colt, Friday telephones the number she was given and explains that Rena and Yarbro are dead. She is advised to come to the City National Bank Building. Once there, she goes to the rooftop and Blake Tarr arrives by helicopter. Tarr explains that "Black Widow" is Senator Hart and that something bad is going to happen on Valentine's Day. Tarr takes Friday to his mansion and they make love.
The next day, Friday and Colt arrive back in Washington and discover all the black politicians are missing. They arrive at Senator Hart's office where a secretary claims the politician left after saying "the walls would come crumbling down today". Realizing this is a reference to the biblical story of Joshua at Jericho, Friday remembers it is also the name of Rev. Franklin's estate. When Friday and Colt step out of the Capitol building, they spot two thugs by their car. Colt tells Friday to telephone Tarr while he distracts the men. Unable to reach Tarr, Friday steals an empty milk truck. She drives to Colt, who has beaten up the two men, and tells him to follow her. However, as Friday drives off, Colt's car refuses to start. Tarr arrives, picks up Colt, and drives after Friday.
At Rev. Franklin's hunting retreat, Friday is stopped by a group of armed men. She smashes a milk bottle over a man's head and speeds for the main house. Charlie appears and orders his men to attack. Once inside the house, Friday finds the missing black politicians conducting a meeting. Friday finds Rev. Franklin to warn him that Hart is coming, but Hart appears and explains he is attempting to build a black caucus and the "walls crumbling down" is a metaphor for ending prejudice. Bullets shatter windows and riddle the walls. As Rev. Franklin hands out shotguns, Hart realizes Charlie and Enos Griffin manipulated him into calling the meeting so they could get all the black politicians in one place to kill them. A man leaps through a window and Friday shoots him, only to discover he is white man wearing "black face." As the battle rages, a helicopter arrives carrying Tarr, Colt and a small army of bodyguards, who catch the attackers in a crossfire. Charlie makes a run for it, but Colt chases him down and knocks him to the ground.
Days later back in Los Angeles, Colt visits Friday and finds her apartment full of gifts from both Tarr and Hart. However, she insists Colt is her "main man."