It’s the season finale, and Non is out to destroy the human race. Superman is now just a pair of boots, so it’s up to Supergirl to save us all by bludgeoning us with hope. And so the season ends as it began: with lots and lots of emotional speechifying.
Non uses the power of Myriad to control all of National City, including a CGI blob that’s allegedly Superman. Supergirl and her crew react to this threat with talking, talking, and more talking.
It’s new Supergirl vs. old Supergirl as Laura Vandervoort guest stars as an evil blue alien who is definitely not Mystique. Also, if you’re interested in not becoming a supervillain, stay the heck away from Winn; he’s a bit of a bad-luck charm.
Supergirl loosely adapts a classic Superman story from the ‘80s (emphasis on loosely), but mostly uses it to advance Astra and Non’s evil plans, which come perilously close to actually making sense.