When a young woman meets a violent death after partying at Verdant Detective Lance and his 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 SETH 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. After Detective Lance uncovers incriminating evidence against him Tommy goes to great lengths to clear his name and the fallout from his actions leads Tommy down a new unexpected path. In a flashback to the island Oliver recalls the lessons he learned from Slade and Shado (guest star CELINA JADE).
In part one of the fifth season finale, Octavia leads her people into war. While behind enemy lines, our heroes must overcome their differences to save Wonkru from extinction.