Plot

Supervillains Harley Quinn, Bloodsport, Peacemaker, and a collection of nutty cons at Belle Reve prison join the super-secret, super-shady Task Force X as they are dropped off at the remote, enemy-infused island of Corto Maltese.

In exchange for lighter sentences, just like the anti-hero team in Suicide Squad (2016), a new batch of Belle Reve's meta-humans strike a deal with the cold head of Task Force X, Amanda Waller. This time, her ragtag band of super-powered convicts--Harley Quinn, Bloodsport, Peacemaker, King Shark, Polka-Dot Man, and Ratcatcher 2--venture into the peril-laden South American island nation of Corto Maltese to find the Thinker: the evil scientist in charge of the mysterious Project Starfish. But, as the band joins forces with an old leader of the notorious team, humankind is on the verge of extinction. Can the expendable Suicide Squad stop the new menace that could mean the end of the world as we know it?—Nick Riganas

Intelligence officer Amanda Waller (Viola Davis) the director of A.R.G.U.S. who runs the Task Force X program, assembles two Task Force X ("Suicide Squad") teams, comprising Belle Reve penitentiary inmates who agree to carry out a mission in exchange for shortened sentences. Sent to the South American island nation of Corto Maltese after its government (which was ruled by the Herrera family for the past 100 years) is overthrown by an anti-American regime. Silvio Luna (Juan Diego Botto, the dictator of Corto Maltese & Mateo Suarez (Joaquin Cosio), the Major General of Corto Maltese had recently taken power in a violent military coup. The entire Herrera family was hanged in a public execution.

Luna is virulently anti-American, and the squads are tasked with destroying the Nazi-era laboratory Jotunheim, which houses the secret experiment "Project Starfish". Starfish is allegedly extraterrestrial in origin. The Squad is assigned to find Dr. Gaius Grieves/The Thinker (Peter Capaldi) since he can lead them to Jotunheim, and they can destroy whatever is going on in there. After hours The Thinker is known to hang out at a strip club called La Gatita Amable.

One team, led by Colonel Rick Flag (Joel Kinnaman) the field leader of the Suicide Squad, & his team including Cory Pitzner / T.D.K. (Nathan Fillion) the Detachable Kid, a meta-human who can detach his arms from his body, Weasel (Sean Gunn) an anthropomorphic weasel, Gunter Braun / Javelin (Flula Borg) a former Olympic athlete who wields javelins as weapons, Mongal (Mayling Ng) an alien mass murderer, Richard "Dick" Hertz / Blackguard (Pete Davidson) an easily manipulated mercenary & Harley Quinn (Margot Robbie), is almost entirely wiped out by the Corto Maltese military upon landing.

Upon arriving, Weasel falls into the water and apparently drowns since nobody knew he couldn't swim. When the Squad makes it to land, Blackguard steps out and reveals he brought the team to the mercenaries waiting for them on the beach. For his troubles, he gets his face blown off. Harley goes in blasting while Boomerang throws his signature weapon to slice some heads off. TDK's arms pop off so he can use them as (ineffective) weapons. The mercenaries retaliate and shoot TDK and Javelin dead. Mongal attempts to bring a chopper down, but it crashes, and she burns to death. Boomerang is impaled with wood and then shredded by the chopper's blades. Harley and Flag go missing while Savant attempts to flee the chaos. Although Waller warns him, she detonates the explosive in the back of his head, causing it to blow up. The military capture Harley Quinn while team leader Rick Flag escapes. Waller had already dispatched her second team to finish the job.

The other team is led by mercenary Bloodsport / Robert DuBois (Idris Elba) a mercenary with a technologically advanced suit that he can use to create different gadgets and transforming weaponry. After being convicted of shooting Superman with a Kryptonite bullet, Bloodsport shortens his prison sentence by joining Task Force X so he can help his daughter Tyla. Waller had threatened to incarcerate Tyla at the Belle Reve for a minor petty theft offense if Bloodsport refused to cooperate. Tyla is embarrassed to have Robert as her father.

Bloodsports team consists of Peacemaker / Christopher Smith (John Cena) a ruthless, jingoistic killer who believes in achieving peace at any cost, King Shark / Nanaue (Sylvester Stallone) A man-eating fish-human hybrid, Polka-Dot Man / Abner Krill (David Dastmalchian) an "experiment gone wrong" in a suit covered with polka dots, George "Digger" Harkness / Captain Boomerang (Jai Courtney) an unhinged Australian thief who wields boomerangs, Brian Durlin / Savant (Michael Rooker) a hand-to-hand combat and weapons expert and Ratcatcher 2 / Cleo Cazo (Daniela Melchior) a thief who inherited the mantle of "Ratcatcher" from her father, along with equipment that allows her to control rats and communicate with them. Bloodsports squad is able to enter the country undetected.

The 2nd team camps in the jungle. Bloodsport is afraid of rats. King Shark tries to eat Ratcatcher 2 but is stopped by Bloodsport. Bloodsport admits that he cannot stand rats. King Shark says that he would never eat his friends, and so Ratcatcher 2 befriends him. The team is dysfunctional as Bloodsport and peacemaker don't get along and try to upstage each other. Flag escaped the carnage on team 1 and is lost in the jungle where he is captured by rebel forces. Waller orders the squad to find Flag, who is being held at a rebel base. Bloodsport is livid that Waller did not inform him about the presence of another squad on the Island.

The squad finds Flag at a base camp for rebel soldiers, and they kill all of them before realizing that the rebels rescued Flag from the military forces and convinces rebellion leader Sol Soria (Alice Braga) to assist them. Despite the group's actions, Soria agrees to help them infiltrate the capital.

Meanwhile, first team survivor Harley Quinn / Dr. Harleen Quinzel is taken captive by the Corto Maltese government and learns of the new regime's plans to use Project Starfish against other nations. Luna has a huge crush on Quinn and wants her to marry him. Quin learns from Luna about Jotunheim and the experiments with Starfish. Quinn shoots Luna dead. Harley is being tortured by Suarez's men for information, but she never budges. When she is left alone with his guard, she snaps his neck with her legs and sets herself free. Harley proceeds to shoot down Suarez's guards before getting her hands on some blades and Javelin's javelin to slaughter her way through the guards

The Squad is being taken by Sol's contact Milton (Julio Cesar Ruiz) to go to a bar called La Gatita Amable where they will find Thinker. The team makes it to the bar, but Nanaue has to stay behind since he will stick out. The Squad drinks and dances before they spot Thinker. They apprehend him, but the military comes in to search everyone since they know that there are Americans in there. Bloodsport sends Ratcatcher outside with Thinker while he, Peacemaker, and Polka Dot Man are all taken in. On the road, the three subdue the gunmen and kill the driver before their van is run off the road. Ratcatcher and King Shark arrive with Thinker in tow.

The squad captures the Thinker / Gaius Grieves (Peter Capaldi), the lead scientist in charge of Project Starfish, and are joined by Harley after she escapes from Suarez (The team was anyways headed to rescue her). They break into Jotunheim with the Thinker's help and begin to rig the facility with explosives. Flag and Ratcatcher 2 enter the underground Project Starfish laboratory with the Thinker.

Flag and Ratcatcher 2 discover that Project Starfish is Starro the Conqueror, a giant alien starfish that creates smaller versions of itself that attach themselves to human faces and take over their bodies like zombies, and there are slews of corpses of Starro's other victims all over the facility.

The Thinker reveals that Starro was brought to Earth by the U.S. government, which has secretly funded the experiments for decades using thousands of Corto Maltese citizens as test subjects. An enraged Flag decides to leak a hard drive containing evidence but is killed by Peacemaker, who is under orders from Waller to cover up the U.S.'s involvement.

The US astronauts brought Starro to Earth, and the US govt made a deal with Corto Maltese Govt to conduct their illegal experiments on their soil and also hired Thinker. Meanwhile, a skirmish between the Squad and the Corto Maltese military leads to Polka-Dot Man accidentally setting off the explosives prematurely. As Jotunheim crumbles, Ratcatcher 2 steals the drive, and Peacemaker attempts to execute her. Bloodsport saves her by shooting Peacemaker and takes the drive.

Starro escapes the destroyed Jotunheim, kills the Thinker and much of the military, and begins taking control of the island's population. Waller tells the squad that their mission is complete and orders them to leave, but Bloodsport leads the team in fighting Starro. Waller attempts to execute them for this, but her subordinates led by Flo Crawley (Tinashe Kajese) brains her with a golf club and has the rest of the team guide the Squad to save the city. After Starro kills Polka-Dot Man, Harley pierces a hole in its eye, allowing Ratcatcher 2 to summon the city's rats to chew Starro to death from the inside. The Squad's heroics are broadcast on the news, and Tyla acknowledges her father as a hero.

With the military diverted, Soria takes control of the government, promising democratic elections. Bloodsport blackmails Waller into releasing him and the surviving squad members and dropping Tyla's charges in exchange for keeping the contents of the drive confidential. Waller reluctantly agrees and the remaining squad members are airlifted out of Corto Maltese.

It is revealed that Weasel, a member of the first team, has survived and runs off into the jungle. Waller punishes her subordinates by assigning them to a new mission with Peacemaker, who is still alive and recovering in a hospital.