Supergirl’s powers are tested when Reactron, one of Superman’s formidable enemies, arrives in National City and targets the young hero. Also, Cat plans to run an exposé on Supergirl.

Personal and professional stress get the better of Kara when she goes too far during a training exercise against Red Tornado, a military cyborg commissioned by Lucy Lane’s father, General Sam Lane. Also, Cat’s tough exterior is shaken by a visit from her judgmental mother, Katherine, and Alex enlists Winn to look into her father’s mysterious death.

Kara must help Hank face his painful past when a White Martian, a member of the alien race that wiped out his people, kidnaps Senator Miranda Crane, an anti-alien politician. Also, Cat's estranged son, Adam, arrives in National City.