With crime at an all time low, Oliver decides to take a break and asks Felicity on a date. However, they're interrupted when a new drug dealer take the name of Count Vertigo and targets the Arrow for death. Meanwhile, Diggle becomes an expectant father and a scientist tries to acquire Queen Consolidated before Oliver can retake his family's business.
Oliver and his team try to find the archer who killed Sara, and discover that a hitman calling himself Komodo had connections to their friends past with the League of Assassins. Meanwhile, Ray continues trying to hire Felicity, and Roy debates whether to tell Oliver why Thea left Starling City.
Felicity tracks Thea to the island of Corto Maltese, and Oliver, Roy, and Diggle got here to bring her back. Meanwhile, Lyla asks Diggle to look into the disappearance of ARGUS agent Mark Shaw, and Laurel looks for an outlet for her frustrations.
Nyssa believes that Malcolm killed Sara and goes after him to avenger her lover's murder. Oliver discovers that he has no choice but to stop her, despite Laurel insisting that he avenger her sister's death. Meanwhile, Thea returns to Starling City and settles in... until Nyssa discovers that she's Malcolm's daughter.
Felicity's past as a crusading hacker is revealed when someone uses a super virus that she designed to bring Starling City to a standstill. Meanwhile, Oliver and Thea work on their new relationship, and Felicity's mother pays a visit.
A killer is murdering his victims and attempting to frame Ted Grant. The Arrow finally comes to his aid after Laurel protests her trainer's innocence. Meanwhile, Roy goes to Felicity for help determining if he killed someone under the influence of Mirakuru.
The Arrow is stalked by an ex-police officer who he rescued during the Mirakuru siege and has become dangerously obsessed with the hero. Meanwhile, Ray asks Felicity to accompany him to a business dinner, and Thea is forced to hire a new DJ for Verdant.
As Barry, Caitlin, and Cisco arrive in Starling City to help with the investigation into Sara's murder, former Suicide Squad member Digger Harkness goes after Lyla. The Arrow and his team need all the help that they can get to stop the boomerang-wielding killer, particularly when he sets five bombs in the city to cover his escape. In the past, Amanda Waller teaches Oliver how to make the hard choices... whether he wants to or not.
Ra's al Ghul sends Nyssa and her lieutenant to Starling City to inform Oliver that the League will kill 50 people a day until Sara's murderer is turned over to them. With time running out, Oliver finally identifies the killer... and realizes that he can never turn them over for execution. Meanwhile, Ray shows Felicity his new project.