Supergirl was in large part a bottle episode this week, with the DEO crew trapped inside their building with not one but two White Martians. These bloodthirsty aliens were after M’gann (guest star Sharon Leal), but J’onn (David Harewood) swore to protect her and the rest of his team stood behind him. A few things happened outside the walls of the DEO, though. In an attempt to avoid her potential feelings for Mon-El (Chris Wood), Kara (Melissa Benoist) planned to celebrate her Earth-landing anniversary with her sister Alex (Chyler Leigh). Unfortunately, Alex already has a date with her new girlfriend Maggie (Floriana Lima), which brings up some abandonment issues Kara wasn’t aware she had.

J’onn experiences a roller coaster of emotions.

J’onn and M’gann are at the center of the action in tonight’s Supergirl, and it seems their relationship has progressed rapidly since their telepathic connection last week. J’onn shape-shifting in order to follow M’gann around borders on creepy, but the sincerity in his explanation and his desire to protect not just her but everyone from the White Martians makes up for it. The actors have an easy chemistry that would strengthen a slowburn relationship, but the show does not afford them that luxury. Instead they are forced to speed through half a season worth of romantic development in a single episode, despite the fact that J’onn had her locked up just a week ago. His love confession was beautifully delivered, for example, but lacked the build up necessary to make it a satisfying turning point in his character. Then, of course, M’gann decides to go back to Mars at the end of the episode – rendering both the confession and the main thrust of the episode moot.

However, the tragic curtailing of M’gann’s storyline doesn’t diminish the magic of the rest of Supergirl this week. M’gann’s ex Armek and a fellow White Martian infiltrate the DEO, leading to a tense and revealing stand-off that showcases how dangerous these characters’ lives can be and how difficult it is to trust your fellow man when your eyes deceive you. Winn (Jeremy Jordan) and Alex both get impersonated by White Martians, which must have been as fun for the actors to play as it was for the audience to watch. Almost every sequence in the DEO was carefully crafted and filled with suspense in the best way, and the lock-in allowed Kara a chance to explore her feelings away from romantic entanglements for a while. It’s been a while since she and Alex had a real heart-to-heart, so hearing Kara pour her heart out to her sister was a welcome change. Even if it was only a shapeshifter pretending to be her sister.

Supergirl can’t stay away from romance for the entire hour, though, so the episode begins and ends with some awkward interactions between Kara and Mon-El. The intergalactic bartender has been making her favorite non-alcoholic drink (as a show of affection, perhaps?), but our heroine still rejects him on account of her hectic work schedule and the kind of person he is. It’s a scene full of secondhand embarrassment, but it also begs the question of what confusion exactly Kara is experiencing. Why wouldn’t she pursue a romance with Mon-El? Not that I particularly want her to, but her later explanation that putting herself out there has backfired rings false. She dated Adam for an episode before realizing she was too busy, and then dated James (a conspicuously absent Mehcad Brooks) for less than one day before deciding she wasn’t interested in him romantically. There doesn’t seem to be an organic reason for Kara to postpone admitting her feelings for Mon-El, since we’re led to believe she has them, other than because the writers feel the time isn’t right yet.

There can never be too much Danvers sisters.

So of course once Alex convinces Kara to take a chance on the boy from Daxam, he has already decided to move on. While that development certainly won’t last, it puts a pin in the relationship for now and will perhaps lead to some jealousy in next week’s episode. Meanwhile, James’ Guardian storyline also took a break this week, since he didn’t even appear onscreen. Kara reminds Winn to stay safe while working with him, but otherwise Supergirl made no effort to work James into the story at all.

“The Martian Chronicles” appeared to be a promising start to an arc for M’gann and a romantic relationship for J’onn, but instead it marked the abrupt ending of both. Though that turn of events was disappointing, the episode was still a strong showing for both actors. Not to mention that it benefitted from keeping several major characters contained in one place, where they could talk out their issues in between well-choreographed fight scenes and some excellent CGI work. Supergirl owes a lot of its heart to the dynamic between the Danvers sisters, and I hope to see future installments highlight that relationship even further.