Keri Adams

In the season premiere, Oliver must transform from vigilante to hero. Diggle and Felicity travel to the island of Lian Yu in search of Oliver, who left Starling City after the devastation of The Undertaking and his failure to avert it. Convinced to return home, Oliver finds that things are in much worse shape than he imagined – Isabel Rochev (recurring guest star Summer Glau) is preparing a hostile takeover of Queen Consolidated, Thea refuses to visit Moira in jail, Roy is trying to fill the void left by the Arrow's absence, and Laurel is working with the District Attorney's office to take down the vigilante. Meanwhile, flashbacks to the island show Oliver's mentors Slade (new series star Manu Bennett), Shado (guest star Celina Jade) and Oliver in a desperate situation.

Oliver discovers a man who goes by the name “The Mayor” is bringing illegal guns in to The Glades, so Oliver sponsors a “Cash for Guns” event to help clean up the city. Unfortunately, The Mayor crashes the event with his gang and seriously injures Sin. The Canary is furious when she learns her friend is in the hospital and sets out for revenge. Meanwhile, Felicity stuns Oliver with a bit of information about the Canary, Donner asks Laurel to dinner, and Diggle reconnects with an old friend.

A seemingly impossible robbery at Queen Consolidated's Applied Sciences Division brings Central City police scientist Barry Allen (guest star Grant Gustin) to town. Citing a similar case back home, Barry offers to help Oliver and his team with the investigation. Oliver senses there is more to Barry than meets the eye, but he's distracted by the similarities between this current case and something that happened on the island. Meanwhile, Felicity takes a liking to Barry, which doesn't go unnoticed by Oliver. Sin asks Roy for help when a friend of hers goes missing. Roy is surprised when Thea not only encourages him to help, but joins the search. Unfortunately, Sin's friend is connected to Brother Blood (guest star Kevin Alejandro), and their search ultimately gets one of them seriously injured.

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 (recurring guest star Seth Gabel) has broken out of prison and is once again distributing his drug. Meanwhile, Moira goes on trial for her participation in the Undertaking. When ADA Adam Donner collapses in court with Vertigo symptoms, Laurel must step in and try the case against Moira - leaving Oliver torn between standing by his family during the trial or catching The Count. The stakes change, however, when Felicity follows a lead and walks straight into a trap set by The Count.

DC Comics' Bronze Tiger and China White wreak havoc on the Glades. Oliver finds out that medicine being sent to Glades Memorial Hospital is being hijacked by thieves – and without an influx of supplies, the hospital will close. When Roy attempts to stop the thieves, he fails and is arrested by Officer Lance. Oliver gets into a heated battle with China White (recurring guest star Kelly Hu) and her new partner, Ben Turner, aka the Bronze Tiger (guest star Michael Jai White), over the supplies. Meanwhile, Laurel makes plans to catch the Arrow, and Thea gives Roy an ultimatum.

Officer Lance's past puts Laurel in danger. Lance learns a criminal named Barton Mathis (guest star Michael Eklund), 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 (guest star Dylan Bruce) seeks the death penalty for Moira. Oliver asks Roy to help him find the Canary (guest star Caity Lotz).