Residents of Supergirl's National City should get their earthquake kits ready - life is about to get a little shaky.

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Kara (Melissa Benoist) has battled an impressive roster of villains in her short time as Earth's newest hero, but the Kryptonian may find herself at a loss when "Human for a Day" combines the search for an escaped alien with a devistating earthquake. In an unfortunate twist for Hank (David Harewood), the episode will cause Alex (Chyler Leigh) to further doubt his motives .

"Kara and her friends must rely on their inner strength and courage when an earthquake strikes National City," CBS teased. "Also, Alex's mistrust of Hank reaches a breaking point when the earthquake traps them in the DEO with Jemm (Charles Halford), a powerful alien escapee."

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Alex's distrust of the DEO leader is not misplaced. Viewers know Hank has an ominous set of glowing red eyes, but the rest of Supergirl's crew has yet to discover Agent Henderson's alter ego. Fresh of the success of The Flash's Harrison Wells/Eobard Thawne/Reverse Flash twist, executive producer Andrew Kreisberg warns viewers it will take some time before anyone learns the truth about the alleged Cyborg Superman.

"We don't want to say too much about it, because I think we had a lot of success with the way we doled out information about Tom Cavanagh's character last year on Flash," Kreisberg teased, according to Entertainment Weekly. "For us, it's so exciting to walk into every scene with him and not know is he there to help you? Or is he possibly there to harm you? That dichotomy and how it plays out is one of the most exciting, unexpected parts of the show."

"Human For a Day" will air on Dec. 7.

Find out more when Supergirl airs Mondays at 8 p.m. ET on CBS.

Tags: Supergirl television CBS