Official Synopsis:

Grant Gustin Crosses Over as “The Flash”

“Worlds Finest” – Kara gains a new ally when the lightning-fast superhero The Flash (Grant Gustin) suddenly appears from an alternate universe and helps Kara battle Siobhan, aka Silver Banshee, and Livewire in exchange for her help in finding a way to return him home, on SUPERGIRL, Monday, March 28 (8:00-9:00 PM, ET/PT) on the CBS Television Network. Grant Gustin crosses over as The Flash.

Stars: Melissa Benoist as Kara Danvers/Supergirl, Calista Flockhart as Cat Grant, Chyler Leigh as Alex Danvers, Mehcad Brooks as James Olsen, David Harewood as Hank Henshaw and Jeremy Jordan as Winslow “Winn” Schott.

Recurring Cast: Jenna Dewan-Tatum as Lucy Lane, Chris Vance as Non, Italia Ricci as Siobhan Smythe, Brit Morgan as Leslie Willis/Livewire,  Christopher Showerman as Tor, Jay Jackson as News Anchor, Dan Warner as Fire Captain.

Guest stars: Grant Gustin as The Flash/Barry Allen, Jamie Kaler as Pundit #1, Samantha Harris as Pundit #2, Zarek King as Young Boy, Sarah Robson as Dr. Amelia Hamilton, Harriet Sansom Harris as Sinead, Dawn Greenidge as Pedestrian Woman.

Written by Andrew Kreisberg and Michael Grassi. Directed by Greg Berlanti.

‘Supergirl/The Flash Crossover’ episode airs Monday, March 28th at 8:00-9:00 PM, ET/PT.