The CW has released the description for the May 19th installment of The Flash titled "Fast Enough".
Season 1 Episode 23 "Fast Enough"
EPIC SEASON FINALE; VICTOR GARBER AND ROBBIE AMELL GUEST STAR
Wells presents Barry with a life-changing choice. Dr. Martin Stein (guest star Victor Garber) and Ronnie Raymond (guest star Robbie Amell) return to help the S.T.A.R. Labs team with this final fight.
Tom Cavanagh as Wells
Grant Gustin as Barry
guest & recurring cast:
Victor Garber as Dr. Martin Stein
Robbie Amell as Ronnie Raymond