Duet

"Duet" is the upcoming seventeenth episode of the third season of The Flash, and the sixty-third episode overall. It will air on March 21, 2017. It will be the second-part of musical crossover between The Flash and Supergirl which was started from the sixteenth episode of second season of "Supergirl".

Synopsis
Barry and team are surprised when Mon-El and Hank Henshaw arrive on their Earth carrying a comatose Supergirl who was whammied by the Music Meister. Unable to wake her up, they turn to Team Flash to save her. However, the Music Meister surprises The Flash and puts him in a similar coma, one that Team Flash can’t cure. Kara and Barry wake up without their powers in an alternate reality where life is like a musical and the only way to escape is by following the script, complete with singing and dancing, to the end.