The tuneful crossover will begin at the end of the Mar. 20 episode of “Supergirl,” but the main vocal action will take place in the Mar. 21 episode of “The Flash.”
That episode, entitled “Duet,” will be directed by Dermott Downs and will feature singing performances from Grant Gustin, Melissa Benoist, Jesse L. Martin, Victor Garber, Carlos Valdes, Jeremy Jordan, and John Barrowman. David Harewood and Chris Wood will have non-singing guest appearances in the episode.