"Supergirl" and its titular heroine have something in common: they both have a tendency to overdo it a little. It (and she) mean well. It (and she) are ultimately endearing, flaws and all. But man, sometimes "Supergirl" lays it on a little thick, and sometimes Kara shouldn't write and mail personal letters on behalf of her boss.

"Strange Visitor From Another Planet" has moments that are among the best that "Supergirl" has offered thus far, including big, terrific moments from the show's two parental figures, H'annk H'enshaww and Cat Grant (David Harewood and Calista Flockhart, both of whom more than rise to the occasion), and two storylines that manage to be compelling and character-driven all at once. Sure, there's another villain of the week (Tawny Cypress, giving a ferocious performance that somehow doesn't feel over-the-top), but this episode sees not one, but two strange visitors who may as well be from other planets. Because these visitors impact people as well as events, it's a gripping hour, even when it overplays its hand -- which it does, and frequently.

The first visitor comes with a storyline that's on the subtler side of things, though it still doesn't offer much in the way of restraint. The episode begins with a voiceover from Kara -- something that doesn't happen often, outside of the opening credits -- as she saves a family strapped inside a forest fire, and we see a pair of mysterious and probably handsome hands reading a letter. Turns out those hands belong to the mysterious and handsome stranger Kara meets in a coffee shop as she picks up Cat's latte. He flirts, she stammers, and before you can say "predictable twist," the latte-flirt/letter-reader shows up in Cat's office because, go figure, he's her son Adam (Blake Jenner, Melissa Benoist's husband and fellow "Glee" veteran). She's pretty surprised to see him, a feeling that increases when she learns why he's there -- the letter she sent, which we heard in voiceover, and which she totally didn't send, because Kara did.

Whoops.

It's lucky for Kara that her instincts about her boss are better than her instincts about her male friends, because Cat promptly fires and then un-fires her. Calista Flockhart is terrific in these scenes, keeping the acerbic, scattered Cat wit we've seen all season while letting out a lot more of the depth and sensitivity that have been only peeked out from time to time. In her first dinner with Adam, Cat babbles on about herself a bit -- a expertly written blend of self-centeredness and nerves, winningly played by Flockhart -- and stays mostly defensive and closed-off from her son. Adam, for his part, is kind of a turd, to use a technical term. He's within his rights to be angry, and showing up at all is a big step, but he seems to have inherited his problems talking about his feelings in a healthy way directly from Mom. Needless to say, it doesn't end well.

That's not the end of the road, however, because in addition to flying and super-strength and ice-breath, Kara's got another superpower: meddling. After she sees how upset Cat is, she declares that she'll find a way to fix it and marches off to help repair this little family. Well-intentioned, weird, and totally unrealistic, but effective. Nothing sells this storyline than one little moment of Flockhart's -- Kara leaves, and as she goes, Cat utters a tiny, broken "Kara," this time pronounced correctly. In a hurry, Kara's got Adam to agree to a second date with his Mom (on the condition, he days, that Kara joins them), and given a second chance, Cat drops the tough schtick and says all the honest things she's clearly wanted to say for years. It's a lovely little scene, and while it strays into maudlin territory here and there, it's still affecting. Solid work, all around.

So, that's the first strange visitor, all reunited with Mom and ready to take Kara out for some Korean barbecue. The second visitor -- a White Martian -- doesn't give in quite so quietly.

H'annk H'enshaww's storyline just gets more interesting week by week. In this episode, we learn a great deal about J'onn's past, which is rife with horrors and heartbreak, and it all comes out when the aforementioned White Martian comes to town to hunt him down (a direct result of J'onn using his powers in last week's episode). The White Martians committed genocide, leading to the slaugter of his people (including his wife and daughters), and they still want nothing more than to see any and all of the Green Martians destroyed. This particular genocidal maniac first rears its head at a political rally of a xenophobic, paranoid politician, Senator Miranda Crane (also played by Cypress). Here's one big instance of "Supergirl" not knowing when to cool it: it's great that they're willing to draw lines between our current political climate, in which elected officials willingly and openly talk about people of other countries as though they're monsters, but they probably don't need to go so far as to say "If we need to build a dome, then build a dome," particularly when they have the same performer merrily talking about watering the ground with blood.

It's incredible how racist they manage to make Senator Crane's dialogue sound, given that she's talking about aliens from out of space. It's also effective in that it makes the (still predictable) twist that the shape-shifting alien took the Senator's form in order to infiltrate the DEO that much easier to buy -- they both say things that just sound ugly. But how much more effective would those sequences have been if they were just a little more plausible? Still, it's a minor complaint, because as scary as the vitriolic language is, it's nowhere as frightening as the sequence in which the White Martian's cover is blown. As directed by Glen Winter (a vet of most of the DC shows, as well as two previous episodes of "Supergirl"), it's a thrilling, violent, blink-and-you'll-miss-it sequence, with Cypress just a hair shy of frothing at the mouth like a rabid animal, not to mention spitting fire. It's a great example of turning one kind of ugliness into another, and it thrills not just because it's adrenaline-laced, but because it's tied to H'annk, and to the White Martian, and to Senator Crane, all at once.

It all leads to a big showdown in the desert, with Alex held hostage, Kara trying to convince H'annk that he shouldn't just a) lay down and die, or b) murder the Martian. Despite H'annk's obvious pain (and Harewood is terrific, in spite of competing with dramatic score he clearly doesn't need), he listens to what his two surrogate daughters are saying, locks up the hateful creature, and lives to H'annk another day.

Things seem headed for a relatively sunny ending, thanks to the real Senator Crane's abrupt turnaround on the issue of aliens (a development that seems ludicrously optimistic, given how deeply rooted such beliefs typically are) and the aforementioned Korean barbecue date on the horizon. But as Kara and Alex watch Crane on the news and swap ice creams, they see something even more surprising -- Supergirl on the news, saving the day. Look out world, here comes Bizarro.