There are two things fans of SupergirlThe Flash, and DC’s Legends of Tomorrow have desperately been waiting for: the musical crossover and the non-flashback/hologram/hallucination return of Leonard Snart (Wentworth Miller). On March 20th and 21st, both those things are happening. Here’s the incredible new batch of synopses!

The first half of the musical crossover will find Kara battling Darren Criss‘ Music Meister and Teri Hatcher‘s mysterious new character. Loyalties will be tested in ‘Star-Crossed’, directed by John Medlen and written by Katie Rose Rogers and Jess Kardos.

TERI HATCHER (“DESPERATE HOUSEWIVES,” “LOIS & CLARK: THE NEW ADVENTURES OF SUPERMAN”) AND KEVIN SORBO (“HERCULES”) GUEST STAR; DARREN CRISS (“GLEE”) MAKES HIS DEBUT AS THE MUSIC MEISTER – A new villain (guest star Teri Hatcher) comes to National City, putting Supergirl (Melissa Benoist) on high alert. Meanwhile, Winn’s (Jeremy Jordan) girlfriend, Lyra (guest star Tamzin Merchant), gets Winn in trouble with the law. Maggie (Floriana Lima) attempts to help Winn but old loyalties get in the way. The Music Meister (Darren Criss) attacks Supergirl.

The second half of the musical crossover brings Mon-El and J’onn over to Earth-1 to seek Team Flash’s help. Barry and Kara enter their very own La La Land in ‘Duet’, directed by Dermott Downs with story Greg Berlanti and Andrew Kreisberg and written by Aaron and Todd Helbing.

'The Flash' Unveils New Logo for Season 4

DARREN CRISS (“GLEE”) GUEST STARS AS THE MUSIC MEISTER IN THE FLASH AND SUPERGIRL MUSICAL CROSSOVER – Barry (Grant Gustin) and team are surprised when Mon-El (guest star Chris Wood) and Hank Henshaw (guest star David Harewood) arrive on their Earth carrying a comatose Supergirl (guest star Melissa Benoist) who was whammied by the Music Meister (guest star Darren Criss). 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.

Just as they gain the power to alter reality, the past will come back to haunt the Legends. The fourth and final member officially joins the Legion of Doom in ‘Fellowship of the Spear’, directed by Ben Bray and written by Keto Shimizu and Matthew Maala.

IT’S WAR — The Legends must devise a plan to retrieve the last remaining fragments of the Spear of Destiny from the Legion of Doom. They find themselves in France at the height of World War I faced with the knowledge that they must destroy the mystical object. They enlist the help of a soldier by the name of John Ronald Reuel Tolkien (guest star Jack Turner) and find that the Spear is leading them into the heart of the war. Meanwhile, the team must all resist the temptation of the Spear, and the return of a former teammate. Victor Garber, Brandon Routh, Arthur Darvill, Caity Lotz, Dominic Purcell, Franz Drameh, Nick Zano and Maisie Richardson-Sellers star. Ben Bray directed the episode written by Keto Shimizu & Matthew Maala (#215). Original airdate 3/21/2017.

Supergirl returns with ‘Exodus’ on March 6th at 8/7c, The Flash returns with ‘The Wrath of Savitar’ on March 7th at 8/7c, and Legends of Tomorrow returns with ‘Land of the Lost’ also on March 7th at 9/8c all on The CW.

Arrowverse Crossover: "Crisis on Earth X"