S2, E7: Oliver is concerned when a mysterious illness sweeps the city, infecting hundreds of people -- including Diggle. Oliver discovers Vertigo in Diggle's blood and realizes Count Vertigo (recurring guest star SETH GABEL) has broken out of prison and is once again distributing his drug. Meanwhile, Moira goes on trial for her participation in the Undertaking. When ADA Adam Donner collapses in court with Vertigo symptoms, Laurel must step in and try the case against Moira, leaving Oliver torn between standing by his family during the trial or catching Count Vertigo. The stakes change, however, when Felicity follows a lead and walks straight into a trap set by Count Vertigo.