The story begins at the end of the Supergirl episode "Star-Crossed", which aired on March 20, 2017, which saw Kara Danvers / Supergirl (Benoist) hypnotized 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.

J'onn J'onzz and Mon-El of Earth-38 arrive on Earth-1 with a comatose Kara Danvers, in hope that Barry Allen and his team can revive her.

Barry wakes up to find himself without his powers in a musical dreamworld where he discovers Kara singing in a nightclub ("Moon River") and where everyone resembles people they know in the real world.

Back in the musical reality, Barry and Kara prepare to sing an original song to appease Cutter ("Super Friend"), but the gang war begins outside.

Main cast members Grant Gustin, Candice Patton, Danielle Panabaker, Carlos Valdes, Keiynan Lonsdale, Tom Cavanagh, and Jesse L. Martin star as Barry Allen / Flash, Iris West, Caitlin Snow, Cisco Ramon / Vibe, Wally West / Kid Flash, Harrison "H.R."

[1] In January 2017, Rachel Bloom revealed that she had penned an original song for the episode, which was titled "Superfriends", and was set to be sung by Gustin and Benoist.

Bloom explained that, "as soon as I heard that they were doing a musical crossover, I e-mailed [CW president] Mark Pedowitz who connected me to Greg [Berlanti] and Andrew [Kreisberg].

Kreisberg commented, "Benj and Justin are the premiere songwriting duo of our time... To have them be a part of our musical episode is beyond our wildest expectations.

He felt the premise was "goofy" but did a good job incorporating the existing continuity from both series, such as building "directly on recent romantic tribulations in Barry and Kara's lives."

He enjoyed the team-up with Kid Flash, Martian Manhunter and Vibe, and was glad the writers did not "attempt to force in a romantic subplot involving Barry and Kara.

Von Doviak concluded, "It's probably logistically untenable for them to ever be more than 'super friends,' but if this show ever needed the positive energy they generate together, now was certainly the time.