Kara (Melissa Benoist) deals with the loss of Mon-El (Chris Wood) by focusing all her energy on being Supergirl and the mysterious new threat against National City. Alex (Chyler Leigh) confesses a secret to Maggie (guest star Floriana Lima) about their impending nuptials. A citizen of National City has a mysterious connection to Kara, and Lena (Katie McGrath) makes a bold move.