Oliver decides it's time for Thea to return home to Starling City, so he packs for Corto Maltese, where Felicity has traced Thea's whereabouts. Lyla (guest star Audrey Marie Anderson) asks Diggle to go with Oliver because one of her field operatives, Mark Shaw (guest star David Cubitt), has gone dark in Corto Maltese and she'd like him to look into it. Feeling responsible for Thea's departure, Roy joins Oliver and Diggle on their journey. Shaw double-crosses Diggle, putting numerous A.R.G.U.S. agents, including Lyla, at risk. Meanwhile, Laurel meets Ted Grant (recurring guest star J.R. Ramirez), and Felicity adjusts to her new job.