King Shark escapes from ARGUS captivity and makes his way to Central City to kill the Flash. However, the hero and his friends are preoccupied with the recent death of one of their own. Meanwhile, Wally resents Barry's presence in his family.

When Barry reaches a dead end in going faster, he decides to travel into the past and trick Eobard Thawne--posing as Harrison Wells--into showing him how to go faster. However, something, in the timestream follows Barry back... and it's not friendly.