As a new enemy emerges seven months after Slade's attack upon Starling City, Oliver battles with the help of his teammate Roy. However, with the Arrow's presence elsewhere someone he had loved dearly is hurt.
Oliver decides it's time for Thea to come back to Starling City, so he packs for Corto Maltese, where Felicity has traced Thea's whereabouts. Lyla asks Diggle to go with Oliver because one of her field operatives, Mark Shaw, has gone dark in Corto Maltese and she'd like him to look into it. Feeling responsible for Thea's departure, Roy joins Oliver and Diggle on their journey. Shaw double-crosses Diggle, putting numerous A.R.G.U.S. agents, including Lyla, at risk. Meanwhile, Laurel meets Ted Grant, and Felicity adjusts to her new job.
Oliver must stop an Arrow-obsessed serial killer, Carrie Cutter, who is convinced that The Arrow is her one true love and will stop at nothing to get his attention. Unfortunately, her way of getting his attention is to kill people. Meanwhile, Ray asks Felicity to be his date for a work dinner with important clients. Thea auditions new DJs for Verdant and meets Chase, a brash DJ with whom she immediately clashes.
The Team's worst fears are realized when Merlyn informs them of Oliver's death. Meanwhile Ray Palmer tests part of his ATOM suit out and Laurel Lance decides to pursue justice outside of the law by taking up the mantle of the Black Canary.
Arsenal and Diggle confront Laurel about trying to step into her sister's shoes and warn her to stop before she gets herself killed. However, the villan Brick kidnaps the city's Aldermen and threatens to kill them all unless the police evacuate The Glades, it's all suits on deck. Meanwhile, Ray steps in to help Lance and the police force fight Brick, showing Felicity a new side of her boss. Malcom tells them that Ra's al Ghul is after his family and they must leave town immediately.
Still operating without Oliver and desperate to stop Brick, Team Arrow is forced to consider Malcolm's offer to help shut Brick down as Malcolm has a personal score to settle with the felon. Roy and Laurel point out that the team could use some help to save the innocents of The Glades, but Felicity is adamantly against it. They look to Diggle to make the final decision. Meanwhile, the flashbacks chronicle Malcolm's descent from kind-hearted father and husband to cold-blooded killer after the murder of his wife.
Malcolm puts Oliver and Thea in a dangerous situation that lands them on Lian Yu with Oliver's former enemy, Deathstroke. A flashback reveals when Oliver and Maseo returned to Starling City to retrieve the Omega bio weapon, and despite being under strict orders from Amanda Waller not to reveal himself to anyone, Oliver looks in on his family, Laurel and Tommy.
Malcolm is captured by Ra's al Ghul and taken to Nanda Parbat. Because of his love for Thea, Oliver considers saving Merlyn. Ray is obsessed with finishing his Atom suit so he can save the city but Felicity fears he is heading down the same path as Oliver and tries to pull him out of the lab.
It's celebration time as Diggle and Lyla get married. However, Deadshot interrupts their honeymoon and tells them the Suicide Squad has been given a new mission - rescue United States Senator Joseph Cray from a hostage situation in the Republic of Kasnia. Amanda Waller breaks down the mission and introduced them to the newest member of the Suicide Squad, Cupid. Meanwhile, Oliver learns about Ray's new Atom costume and the two have a heated stand-off. Felicity and Ray hit a rough patch.
During an attack on the mayor's office, Ray is critically injured. Felicity is pleasantly surprised when her mother, Donna Smoak, shows up at the hospital to offer her support. With the SCPD out in full force looking for the assailant, Oliver and his team work hard to stay one step ahead of the police to find the man responsible. However, things come to a head when Ra's al Ghul kidnaps Captain Lance.