Supergirl, like any good sci-fi show, finally did an episode that was a giant homage to John Carpenter’s The Thing. On Monday’s episode, those White Martians that Miss Martian warned us about last week came looking for her, and they used their shapeshifting abilities to seed chaos and distrust amongst the trapped D.E.O. agents. At the end of the hour, J’onn loses M’gann to the White Martians — but it’s a bittersweet loss, not a deadly, tragic one.

After M’gann’s ex comes threatening her, the good White Martian tries to flee or give herself up to avoid any harm befalling her newfound and increasingly close friends. J’onn, of course, won’t have it, but his attempt to bring her to the safety of the D.E.O.’s HQ backfires when two of the invaders stealthily infiltrate the high-tech facility. We’re then treated to some suspenseful scenes as the group tries to figure out which one of them is actually a White Martian in disguise, and a genuinely exciting twist when J’onn and M’gann realize that there are two White Martians inside, not one.

This reveal cuts Kara and faux-Alex’s heart-to-heart short (Kara’s love life is not going great, at the moment) to make way for some action. Kara is able to best her opponent while J’onn and M’gann, who seems to have embraced her Green Martian form as more than just a disguise, defeat their foe as well.

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Miss Martian as seen in 'Supergirl.'
Miss Martian as seen in 'Supergirl.'

Sure, Alex missed that Barenaked Ladies concert that Maggie got her tickets for, and things with Kara and Mon-El are still crummy, but at least J’onn and M’gann seem like they’ve taken their relationship to the next level. J’onn’s new, deep bond with M’gann makes what she does next that much more difficult to bear: She leaves.

M’gann wants to return to Mars to try to reach out to any good White Martians. It may be a suicide mission, but it’s a noble quest. It just leaves J’onn down in the dumps and Supergirl down one more powerful ally. Since next week it looks like she’ll be facing down with a Luthor, Kara might wish she had the help.

Photos via Warner Bros. Television