Diggle and Felicity convince Oliver to return to Starling City despite the fact he blames himself for Tommy's death. He only returns to save Queen Consolidated, but soon becomes embroiled in a crisis when several men using the name of The Hood start killing the rich to get revenge for the Undertaking... and Thea Queen is their next target. Meanwhile, in the past on the island, Oliver, Slade, and Shado kill Fyers and his men, but soon receive a visit from someone new.
When criminals hijack medical supplies meant for The Graves, Oliver decides that the Hood should put a stop to the robberies. However, China White is responsible and has a new partner: the Bronze Tiger. Meanwhile, alderman Sebastian Blood continues to try to rally the city to help those in The Glades and considers an alliance with Oliver.
Lance learns a criminal named Barton Mathis, whom he put away years ago, broke out of prison during the quake and is back to torturing and murdering women. Felicity offers herself as bait so Arrow, Diggle, and Lance can catch this villain, but the plan goes awry. Furious, Mathis kidnaps Laurel in retaliation and plans to murder her while Lance watches. Meanwhile, Thea and Oliver are stunned when District Attorney Adam Donner seeks the death penalty for Moira. Oliver asks Roy to help him find the Canary.
A new crime lord, The Mayor, plans to take over Starling City using stolen military weapons. While the Hood tries to stop him, he encounters Black Canary and discovers who she really is. When The Mayor injures Black Canary's sidekick Sin, the female vigilante joins forces with the Hood to take the gunrunner down. Meanwhile, Quentin confronts Diana about her drinking problem, and in the past, Oliver is interrogated about the corpses on the island.
Oliver puts Sara Lance up at the manor and soon discovers that she doesn't want to contact her family... both because she would put them in danger, and because she become a killer since the last time they saw her. Meanwhile, the League of Assassins send men to bring Sara back, alive or dead. And Oliver discovers that Laurel will be sitting second chair for his mother's trial.
Amanda Waller sends A.R.G.U.S. agents to kidnap Diggle. Waller informs Diggle that Lyla has gone missing after following a lead on Deadshot in Moscow. When Diggle tells the team he's headed to Russia to rescue Lyla, Oliver and Felicity decide to join, but things get messy when Isabel shows up on the tarmac and insists on joining Oliver's "work trip." Meanwhile, Moira's lawyer, Jean, tells Thea that dating Roy, a known criminal, is hurting her mother's case.
Oliver is concerned when a mysterious illness sweeps the city, infecting hundreds of people, including Diggle. Oliver discovers Vertigo in Diggle's blood and realizes The Count has broken out of prison and is once again distributing his drug. Meanwhile, Moira goes on trial for her participation in the Undertaking. ADA Adam Donner collapses in court with Vertigo symptoms so Laurel must step in and try the case against Moira. Oliver is torn between standing by his family during the trial and catching The Count. However, things change when Felicity follows a lead and walks straight into a trap set by The Count.
When a superhumanly strong thief robs a Queen Consolidated warehouse, Central City police scientist Barry Allen comes to Starling City to investigate the case. However, despite his close working relationship with Felicity, Oliver suspects that there's more to the young scientist than meets the eye. Meanwhile, Sin asks Roy to help investigate the disappearance of a friend. In the past, Oliver, Shado, and Sara try to get Slade to the submarine so they can use the serum to save his life.
After a fight with Cyrus Gold AKA the Acolyte, Oliver is drugged and left for dead. Determined to cure him, Felicity makes a risky decision. The cure causes Oliver to hallucinate, and what he sees forces him to confront his past. Meanwhile, Barry continues to help Felicity, and their connection grows stronger. The Arrow asks Lance to look into Gold, but when the stakeout on Gold goes bad, someone is killed. Roy is captured and tortured by Brother Blood.