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 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, Shado and Oliver in a desperate situation.

When a dangerous criminal from Lance's past escapes from prison, Felicity offers herself up as bait so Arrow, Diggle and Lance can capture him...but plans go awry.

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.

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.

The Count has a new scheme to turn Starling City's residents into clients by addicting them to a new drug and then selling them Vertigo to cure it. among those stricken are Diggle and DA Donner, who collapses in the middle of presenting his case against Moira.

A bomber nicknamed Shrapnel has set his sights on Sebastian Blood, and Oliver dons his mask to protect his newfound ally. Meanwhile, Laurel investigates Sebastian's aunt who is locked up in a mental institution, and Thea learns about Roy's newfound superstrength.

When her father won't believe her accusations against Sebastian, Laurel turns to the Arrow for help. Oliver has his own doubts about Laurel, particularly when she is arrested on a charge of drug possession. Meanwhile, Roy sets out to test his new abilities but goes berserk, putting a man in the hospital.

The Huntress returns and takes hostages at the courthouse when her father is arrested. Laurel is among those taken, which prompts her sister, the Canary, to battle the Huntress in an epic confrontation. Meanwhile, Roy tries to keep Thea safe, but he doesn't like the way he is forced to do it.