what episode is the flash and supergirl crossover musical
Duet (The Flash) "Duet" is the seventeenth episode of the third season of The CW television series The Flash, which aired on March 21, 2017. The episode was written by Aaron Helbing and Todd Helbing from a story by Greg Berlanti and Andrew Kreisberg, and was directed by Dermott Daniel Downs. The episode features a musical crossover with Supergirl and reunites Grant Gustin and Melissa Benoist with their former Glee co-star Darren Criss, who portrays the Music Meister. Jesse L. Martin also reunites with Jeremy Jordan, with whom he previously worked in the 2012 musical film Joyful Noise. The story begins at the end of the Supergirl episode "Star-Crossed", which aired on March 20, 2017, which saw Kara Danvers / Supergirl (Benoist) being put into a coma by Music Meister, with Mon-El (Chris Wood) and J'onn J'onzz / Martian Manhunter (David Harewood) bringing her to Earth-1 in hope that Team Flash can save her.
Crisis on Earth-X "Crisis on Earth-X" is the fourth annual Arrowverse crossover event, featuring episodes of the live-action television series Supergirl, Arrow, The Flash, and Legends of Tomorrow on The CW. The crossover began on November 27, 2017, with Supergirl and Arrow, and concluded on November 28, with The Flash and Legends of Tomorrow. In "Crisis on Earth-X", Barry Allen and Iris West's friends come to Central City for their wedding, only for the proceedings to be interrupted by interlopers from analogous universe of Earth-X where World War II was won by the Axis Powers.