Supergirl goes with Hank to Mars in response to M'gann's telepathic request for help. Meanwhile, Maggie invites her estranged father Oscar to her and Alex's wedding shower that's sponsored by Eliza.

Morgan accuses Lena of poisoning the children of National City with the lead bomb she used to drive off the Daxamites. Kara and Sam work to clear their friend's name. Meanwhile, Maggie and Alex break up.