In flashbacks, Oliver and Talia kill an illegal drug merchant from Robert Queen's list. Talia again presses Oliver to return home, but he chooses instead to help Anatoli kill Gregor.

During the S.T.A.R. Labs incident, CCPD undercover officer Tina Boland develops a sonic scream after watching her partner die at the hands of drug dealer Sean Sonus. In the present day,

Oliver welcomes the seemingly-revived Laurel into the team; but it becomes clear that she is Laurel’s Earth-2 doppelganger, having been broken out of S.T.A.R. Labs by Prometheus. Laurel escapes and calls Oliver for an arrangement, ending in her capture. Learning about Paul, Rene convinces Curtis to focus on his capabilities, not his flaws. Laurel is captured, and Oliver places her in an A.R.G.U.S. facility, hoping to change her one day. Oliver reveals his plans to follow (Earth-1) Laurel's dying wish, to find a new Black Canary. In a bar in Hub City, a woman with a sonic scream stops an attempted assault in a bar. Meanwhile, Oliver convinces Adrian to represent John. The latter’s corrupt superior, General Walker, arrives to assume his custody; but Adrian manages to bring John to his own jurisdiction. In flashbacks, Gregor, the Bratva traitor, attempts to force Oliver’s obedience; but the latter is rescued by a female archer named Talia.

Prometheus obtains further intel about the team from Evelyn. He then attacks and hospitalizes Curtis, injecting him with a tuberculosis vaccine developed by Justin Claybourne, a corrupt pharmaceutical manufacturer named on Oliver's former kill list. Flashbacks show that Oliver killed Claybourne after discovering that he financed a TB epidemic, then raised the price on his drug to boost his company's profits. When the team tracks down Prometheus, Evelyn reveals her true allegiance and escapes with Prometheus. Investigating Prometheus on his own, Billy sends information he discovers to Felicity just before the villain captures him. The information turns out to be about Claybourne's illegitimate son, who may now be seeking retribution. Oliver deduces that Prometheus is at Claybourne's former office building and goes there alone. He finds that Prometheus has staged it to resemble Oliver's prior attack. Oliver kills Prometheus, only to discover he has actually killed a gagged Billy, whom the real Prometheus set up as himself to trick Oliver. Curtis's husband Paul leaves him after discovering Curtis is a vigilante; Felicity mourns Billy's death; Diggle is recaptured; and Oliver finds Laurel Lance alive and well inside the lair.

Oliver finds himself back at Queen Manor; both his parents are alive, he is about to be married to Laurel Lance, and Diggle is the Hood. However, it is revealed that he, Diggle, Thea, Sara and Ray are all being held unconscious inside pods aboard a Dominator spaceship. Meanwhile, Felicity, Curtis and Cisco Ramon try to hack into the Dominators’ mainframe using a piece of their technology. The team recovers a necessary device with the help of the Flash and Supergirl, and they manage to locate the others. Oliver begins seeing flashes of his former life, as do Sara and Ray. All five captives soon realize that they are inside a shared hallucination. Their escape attempt is blocked by manifestations of Malcolm Merlyn, Deathstroke, Damien Darhk and their mercenaries, all of whom are defeated by the captives. The captives then leave the dream and awaken inside the ship. Escaping in a shuttle, they are rescued by the Waverider. Ray deduces that the Dominators were gathering information from their minds, using the hallucination as a distraction, to help them complete a special “weapon”. The team learns that the Dominator mothership is headed toward Earth.

This episode continues a crossover that begins on The Flash season 3 episode 8 and concludes on Legends of Tomorrow season 2 episode 7.

A new vigilante appears in Star City, known as "Vigilante", one who kills criminals in cold blood. Quentin tenders his resignation as Deputy Mayor. He later tells Thea about the throwing star and his drunken blackouts, but believes he is being set up. The team intercepts the Vigilante during a bank robbery, but he gets away, as does Eric Dunn, the head of the robbers. D.A. Chase forces one of the other robbers to reveal Dunn's location, and Green Arrow saves him from the Vigilante. Thea convinces Quentin to go into rehabilitation, while Oliver and Susan start getting closer. The team poses as the bank robbers to lure in the Vigilante, who again escapes even after Oliver defeats and nearly unmasks him. Thea tells Oliver about Quentin and the possibility of his being framed; they deduce that Prometheus must know Green Arrow's identity. Evelyn is revealed to be working for Prometheus. In flashbacks, Kovar introduces Oliver to his servant Galina, Taiana's mother. He also claims that the Bratva has only been using Oliver for their own ends, including making a deal with him. Kovar then releases Oliver back to the Bratva.

Oliver, Diggle and Felicity privately track Prometheus, who starts killing seemingly random civilians with throwing stars. A news report on the killings causes tension in the city and angers the recruits, since they were not informed. Felicity steals one of the stars from Billy to examine. A pattern between the victims relates to Oliver's list from when he started out. This further angers the recruits, Evelyn most of all, as they did not know about Oliver's "kill list" from when he first returned. Felicity uses the pattern to predict future victims, and the team splits up. Evelyn encounters Prometheus and engages him, managing to cut his arm before being overpowered. Oliver then arrives, but Prometheus escapes. Meanwhile, Thea discovers that Quentin never quit drinking. Evelyn reconciles with Oliver, and Felicity tells Billy that she works with the Green Arrow, which intrigues him. She later tells Oliver that evidence she has discovered suggests that Prometheus could be an SCPD officer; Quentin is shown awakening from an alcohol-induced sleep with a slash across his arm and a throwing star in his possession. In flashbacks, during a Bratva operation, Oliver is abducted by Kovar's men and taken to him.

Oliver rescues Rene, who tells him that he gave up Green Arrow's true identity to Church. Church plans to kill Oliver as the Mayor instead of the vigilante. Diggle rejoins the team and recommends bodyguard Christopher Chance, the "Human Target", to help them. Christopher impersonates Oliver at the City Hall and fakes the Mayor's death when Church's mercenary attacks. The team realizes that Church plans to consolidate the drug traffic of five cities through Star City, needing Green Arrow eliminated for his plan to succeed. Oliver and his team, joined by Diggle and Christopher, raid Church's meeting and capture him and other crime lords. Oliver publicly claims that his faked death was part of a sting operation. Prometheus kills Church during transport, despite Church telling him Green Arrow's identity. Television reporter Susan Williams obtains evidence that Oliver was in Russia during the time he was supposedly stranded on the island. Meanwhile, Oliver finds out that Felicity is dating Billy Malone, a police detective recently assigned to the Anti-Crime Unit. In flashbacks, Oliver is ambushed by other Bratva members. However, the men are killed by Christopher, whom Anatoli had hired to protect Oliver.

Oliver's team captures an associate of Church's and delivers him and his loot to the SCPD. Afterward, Rory formally leaves the team saying that he cannot work with Felicity. Oliver leaves Star City to help Lyla break Diggle out of prison, over Felicity and the team's objections. Quentin and Adrian personally deliver the evidence to the SCPD, which turns out to be a disguised bomb. The explosion allows Church's group to break in and steal weapons and equipment. Oliver infiltrates a federal prison and locates Diggle, who agrees to escape to safeguard Oliver. Oliver takes him and Lyla to a H.I.V.E. safe house. Felicity attempts to reconcile matters with Rory. She and the team determine that Church plans an assault on the SCPD's anti-crime unit, where Adrian is interrogating Church's man. Rory rejoins the team, and they help everyone inside escape the attack. However, Curtis is injured and Church captures Rene, intending to torture him to death. Oliver returns and vows to rescue Rene, while Adrian decides to trust the vigilantes' motives. In flashbacks, Anatoli tasks Oliver with gaining information from, and then killing, an associate of Kovar. Oliver completes the assignment, and Anatoli welcomes him into the Bratva.

Green Arrow investigates a new drug, "Stardust", but still believes his team is not ready for the streets. While he is being informed about Prometheus, Rene and Evelyn secretly raid Stardust dealer Derek Sampson's warehouse. The raid goes wrong and Sampson ends up with superhuman strength and an inability to feel pain. Oliver learns what happened from District Attorney Adrian Chase, convincing him that he still cannot trust his recruits. Felicity advises him to accept the recruits as they are, and Green Arrow finally uses his new team to stop Sampson from creating more superhumans. Oliver also publicly endorses Thea's decision to appoint Quentin as Deputy Mayor after negative news stories almost cause her to resign. Felicity admits to Rory, the Ragman, that she was the one responsible for Havenrock. Diggle is incarcerated and hallucinates Floyd Lawton as his cellmate due to guilt over killing his brother. Afterward, he tells Lyla he will not fight the charges against him, so she asks Oliver to help her break Diggle out of prison. Flashbacks focus on Anatoly teaching Oliver the need to trust his brothers in the Bratva.