After Thea gets in trouble with the police, Oliver turns to an old flame - now a vice cop - to help track down the creator of a new designer drug with lethal after-effects.

Vertigo is again appearing on the market even though The Count, who created the drug, is still in a psychiatric hospital. Soon after Oliver confirms that he's still there, he somehow manages to escape. The Count's psychiatrist says his patient overpowered him and has concluded that his insanity was just a ruse. The police suspect Tommy may be dealing drugs from the club and Det. Lance gets a search warrant. Oliver is not sure what to believe and Tommy, feeling his onetime friend has no respect for him, quits. He turns to his father for a job. Digg gives information about Deadshot to a former intelligence colleague. On the island meanwhile, Oliver begins to learn how to use a bow.

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 The Count has broken out of prison and is once again distributing his drug. Meanwhile, Moira goes on trial for her participation in the Undertaking. ADA Adam Donner collapses in court with Vertigo symptoms so Laurel must step in and try the case against Moira. Oliver is torn between standing by his family during the trial and catching The Count. However, things change when Felicity follows a lead and walks straight into a trap set by The Count.