Supergirl will travel back to Krypton - or at least a warped version of Kara's (Melissa Benoist) home planet — on Monday's episode, "For the Girl Who Has Everything."

The alien superhero will fall into a coma-like daydream, thanks to a mysterious plant called the Black Mercy. In that state, she believes that she's back on Krypton, which was never destroyed, and that she got to grow up with her family like she always wanted.

"She's basically, in a sense, tricked into believing that everything is hunky-dory, even though her mom and dad are still very much dead," Supergirl co-star David Harewood explains to TVGuide.com. "She makes a decision to come out of that, to leave that, because she knows it's not real, even though it's very seductive. She knows that she doesn't really belong there."

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The encounter with the Black Mercy comes very soon after Kara helps Hank/J'onn J'onzz (Harewood) overcome his own homesickness for Mars in the wake of a White Martian attacking Earth. The experience taught J'onzz that he can't look back, and perhaps Kara can learn from that.

"She understands that even though she's presented with her history and her backstory, there's something not quite right about it, and [she] decides to leave it in order to go back to reality, where she is alone," Harewood says. "She understands that. It makes her stronger making that decision, because it would be easy to stay in a Utopian existence."

Supergirl airs Monday at 8/7c on CBS.

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