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- Writers: Ali Adler, Greg Berlanti, Andrew Kreisberg
- Stars: Melissa Benoist, Mehcad Brooks, Chyler Leigh, Jeremy Jordan,
Supergirl's powers are put to the test when one of Superman's most formidable enemies, Reactron, shows up in National City to take her down. In the meantime, Cat makes plans to run an expose on Supergirl.