Supergirl takes a break from battling Reign this week in order to focus on how Sam (Odette Annable) is handling her blackouts. However, “For Good” also spends some time re-calibrating Lena’s (Katie McGrath) moral compass and delivers a decisive conclusion to her ongoing Morgan Edge saga. Both of these stories lead to some strong moments for the ladies, but also short-change the momentum gained from learning about other worldkillers.

I get by with a little help from my friends.

Since Sam confessed her gaps in memory to Alex (Chyler Leigh) last week, the latter brushes up on her long-forgotten doctor skills in “For Good” – complete with a not so subtle nod at her Grey’s Anatomy character. Seeing as there’s no reason Sam couldn’t get herself checked out by a practicing neurologist, this seems like a plot convenience to get Alex and Sam to bond a little more. But I’m not going to complain too much, because the two women work beautifully together. Annable has turned Sam into a fully-formed character full of gumption and pathos, and her heart-wrenching fears about being sick and leaving her daughter behind are some of Supergirl‘s best acted moments. And Leigh is the show’s star performer, so of course she holds her own and elevates their scenes together.

Despite the tests – which do eventually get handled by doctors who weren’t trained at Seattle Grace – proving that there is nothing medically wrong with Sam, she’s still understandably shaken and needs her friends more than ever. The only problem is that she’s never relied on anyone but herself before, and it’s a struggle for her to open up to Kara (Melissa Benoist) and Lena. But she does eventually, and we are treated to a few very powerful scenes that establish the deep friendship between the four ladies. It’s yet again another shortcut that bypasses a lot of the actual relationship building, but the actresses make it work and it certainly makes the dramatic irony of Sam being Reign all the more painful. There has to be a way to separate the two before defeating the worldkillers, right? Because if not, Supergirl is in for a massively downer ending this season.

No, I still don’t know why Kara won’t tell Lena her secret.

Meanwhile, Lena is dealing with a crisis of her own in “For Good” – and unfortunately it revolves around Morgan Edge. This character has been a thorn in my side since he appeared, but at least he finally serves a real purpose in Lena’s story. After goading her into nearly killing him the last time he showed, he now blames her for the latest attempt on his life. And while she has Kara and James (Mehcad Brooks) backing her up and believing in her, she still veers dangerously close to falling to the dark side after he returns the favor by poisoning her coffee. Though at times her emotional one-eighty feels a little abrupt, it’s understandable due to the life-threatening stress she’s under.

To make matters worse, Lillian Luthor (guest star Brenda Strong) emerges once more to tempt Lena. She even admits to being behind the attempts at assassinating Edge, hoping that she can coax Lena into becoming a mother-daughter murder duo. The scenes between McGrath and Strong cackle with intensity, making up for the slight ridiculousness of the situation. What would possess Lillian Luthor to not only risk capture, but also whip out a Lexosuit in full view of everyone in order to murder Morgan Edge? Guess she really loves her daughter. And in the end, it is that love amidst the chaos that lets this part of “For Good” shine. Lena learning to accept her Luthor traits without letting them control her, and her mother managing to prove her affection in a rather twisted way, save the plot from feeling overblown and trite.

The only movement on the Reign front was Winn (Jeremy Jordan) narrowing down possible worldkiller candidates – though of course Sam was not included in the list – and Kara immediately knowing that Julia Freeman had to be one of them. While this sets up their upcoming confrontation, I can’t help but feel that the episode would have been better served if Supergirl had waited to include Purity’s awakening as part of this week’s tag so that there was more of a balance. Aside from that, Mon-El (Chris Wood) had the same conversation they’ve had for the last three episodes about still caring for each other despite things being awkward, and it’s starting to feel like the show is spinning their wheels on that romance until they can get rid of Imra. And while James got to play hero when his girlfriend was in danger, even putting on the Guardian suit to shake Morgan Edge down, he and Lena also seem to have stalled since their first kiss. There’s a hint at possible workplace tensions interfering with their relationship, but it hasn’t gone anywhere yet. “For Good” is a collection of powerful moments within a somewhat sloppy framework, but there is still plenty to enjoy.

Supergirl airs Mondays at 8/7c on the CW.