Oliver decides it's time for Thea to come back to Starling City, so he packs for Corto Maltese, where Felicity has traced Thea's whereabouts. Lyla asks Diggle to go with Oliver because one of her field operatives, Mark Shaw, 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, and Felicity adjusts to her new job.

When a cyber attack brings Starling City to its knees, Oliver and Felicity are pushed to their limits to contain the destruction. Life gets even more complicated for Felicity when her mother, Donna, stops by for a surprise visit. Meanwhile, Ted Grant questions Laurel's motives, and Thea buys an apartment with Malcolm's "estate" money, which infuriates Oliver.