"Unfinished Business" - When a young woman meets a violent death after partying at Verdant, Detective Lance and his new partner, Detective Hilton (guest star Roger Cross) inform Oliver and Tommy that she was on the drug Vertigo. Oliver immediately pays a visit to the mental institution where The Count (guest star Gabel) is locked up, but finds he is in no condition to deal drugs. However, when The Count escapes and Starling City is flooded with even more Vertigo-related violence, Oliver and Diggle make it their mission to track him down. Michael Offer directed the episode written by Bryan Q. Miller & Lindsey Allen.
Episode 19 of Arrow ("Unfinished Business") airs on Wednesday, April 3rd on The CW.