At the very end of last night’s episode of Supergirl, Kara (Melissa Benoist) got whammied by the mysterious Music Meister (Darren Criss). He then used her inter-dimensional extrapolator to open a breach to Earth-1 and go after the Fastest Man Alive (Grant Gustin). Tonight on The Flash, J’onn (David Harewood) and Mon-El (Chris Wood) are going to bring Kara over to Earth-1, as well, to ask for Team Flash’s help to wake up the Girl of Steel (and presumably warn Barry).

The humongous photo gallery for the episode is jam-packed with different characters from different shows from different realities. We have Barry and Kara unconscious at STAR Labs and their friends trying to save them. We also see the musical dream world the two superheroes find themselves trapped in. Get ready to meet mob bosses Martin Stein (Victor Garber) and Digsby (Jesse L. Martin), aka Joe, and their daughter Millie Floss (Canidce Patton), aka Iris; the man Millie’s in love with, Tommy (Chris Wood), aka Mon-El, who’s the son of rival mob boss, Malcolm Merlyn (John Barrowman) (a la West Side Story); and the pianist, Winn (Jeremy Jordan), and busboy, Pablo (Carlos Valdes), aka Cisco, who work at Malcolm’s bar.

The trailer for the episode has Music Meister lay out the rules of the movie musical to Kara and Barry: 1) stick to the script and 2) don’t die. Oh! And did we mention that Supergirl and The Flash don’t have their powers?

Photo Gallery & Extended Trailer for 'The Flash' Season 4 Premiere

‘Duet’ airs tonight at 8/7c on The CW.