Kara gains a new ally when The Flash, a super-fast speedster from a parallel universe, arrives and asks for her help getting home. But first the two must team up to stop Siobhan — a.k.a. “Silver Banshee” — when she breaks Livewire out of the D.E.O. and goes after Cat.

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SUPERGIRL GAINS A NEW ALLY WHEN THE LIGHTNING-FAST SUPERHERO THE FLASH HELPS HER BATTLE LIVEWIRE AND SILVER BANSHEE, ON "SUPERGIRL," MONDAY, MARCH 28

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.

REGULAR CAST:

Melissa Benoist (Kara Danvers/Supergirl)
Calista Flockhart (Cat Grant)
Chyler Leigh (Alex Danvers)
Mehcad Brooks (James Olsen)
David Harewood (Hank Henshaw/J'onn J'onzz)
Jeremy Jordan (Winslow "Winn" Schott)

RECURRING CAST:

Jenna Dewan-Tatum (Lucy Lane)
Chris Vance (Non)
Italia Ricci (Siobhan Smythe)
Brit Morgan (Leslie Willis/Livewire)
Christopher Showerman (Tor)
Jay Jackson (News Anchor)
Dan Warner (Fire Captain)

GUEST CAST:

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