Police scientist Barry Allen travels to Starling City to investigate a seemingly impossible robbery from Queen Consolidated's Applied Science Division, and Felicity takes a liking to him... much to Oliver's dismay. Meanwhile, Sin asks Roy for help tracking down a missing friend, and Thea joins her boyfriend in the hunt, only for one of them to be injured.moreless
After Walter's mind is damaged by Windmark's telepathic probe, the team goes to Walter's old Harvard lab to find the information they need to defeat the Observers.
In the year 2036, Peter, Astrid, Walter, and Etta set out to find Olivia and free her from amber. Once they do, they discover she holds the key to finding the plans for a weapon to defeat the Observers... but Walter is captured and interrogated for the same information.moreless
Kate is asked by Justin to negotiate a case for the FBI but things aren't as simple as they appear.