The time is fast approaching for the Undertaking to occur and Malcolm Merlyn begins to tidy up the loose ends, beginning with the scientists at UNIDAC. Oliver and Digg trick Moira into telling just what the Undertaking is about. Oliver realizes that even if he manages to eliminate everyone on his father's list he has only, in his own words, eliminated the symptoms and not the disease. Felicity locates the UNIDAC device - sort of. Thea and Roy's relationship comes to head when they are unable to locate the vigilante. Walter files for divorce. Laurel and Oliver begin a new relationship. In a flashback to his time on the island, Oliver learns just what Edward Fyers' plan is.

Oliver, Canary, Diggle, and Felicity return to the lair and find Slade waiting for them. An epic battle breaks out and one member of Team Arrow is sent to the hospital. Thea hits her breaking point, but just as Oliver is about to reach her, Slade intervenes and Oliver is faced with a choice - his battle with Slade or his family. Meanwhile, Laurel struggles with a new secret.