While preparing his case against Cary, Finn discovers a potentially devastating piece of evidence which could have ramifications for Alicia and Peter. Eli becomes wary when a new prospective candidate emerges in the race for State’s Attorney.
A suspicious Clarke confronts President Dante Wallace and demands answers. Kane interrogates one of The 100, and Abby performs emergency surgery. Meanwhile, Octavia resorts to violence to find Lincoln.
Claire allows Phil to take over Halloween this year, so he decides to turn the house into AwesomeLand. Cameron gets overwhelmed by the day’s activities. Mitchell has closing arguments for a huge case, and it doesn’t help that the stenographer is dressed like a spider.
A furious Nyssa confronts Oliver about Sara. When Oliver learns Malcolm Merlyn is alive, he suspects Merlyn killed Sara. Oliver and Nyssa join forces and go after the Dark Archer, intent on bringing Sara’s killer to justice. Laurel keeps her distance from Nyssa, as she blames her sister’s death on her involvement with the League of Assassins. Meanwhile, Oliver and Roy work on repairing their respective relationships with Thea, who has returned home. Nyssa discusses Oliver with her father, Ra’s al Ghul.
Frankie and Mike are surprised when Brick invites a girl over to the house to hang out; Sue tries to organize a screening of a holiday classic in a pumpkin patch; Axl is locked inside the library.
The world turns against S.H.I.E.L.D. when Hydra impersonates them to attack The United Nations, and an unexpected enemy leads the charge to bring about their downfall.
The Flash stops a robbery but the culprits get away after shooting a guard, and The Flash chooses to save the man instead of following the criminals. Joe shows Barry a book of suspects and Barry identifies Leonard Snart as the leader of the group. Snart revises his plan to steal the Kahndaq Dynasty Diamond and gets a boost when he gets his hands on a stolen “cold gun,” which could kill The Flash. Dr. Wells is furious when he finds out that Cisco built the cold gun without telling anyone and now it’s missing. Meanwhile, Iris is getting the silent treatment from Joe because of her relationship with Eddie.
When a web celebrity is murdered, Castle and Beckett explore the flashy world of internet fame. But when the killer posts pictures from the crime scene on a photo-sharing site, they realize they are up against a social media sociopath who may strike again.
Carrie tries to earn the trust of a frightened asset. On his way out of town, Saul catches a break when he spots a familiar face. Quinn and Fara stake out a new suspect.
Elsbeth and Alicia put their fight on hold when they both have clients facing economic espionage charges. Diane battles her former partners over office space.