To stop Non from wiping out Earth's population, Supergirl has no choice but to sacrifice her life. Before she does so, Kara says goodbye as best she can to her friends without telling them the truth and inciting a panic.
After a seemingly Kryptonian pod crashes in National City, Superman comes to visit his cousin. While the two of them try to determine if Lena Luthor--Lex's sister--is up to no good, Kara wrestles with her personal life.
Cadmus creates a second Metallo and declares war on any aliens on Earth. Meanwhile, Kara finds her new boss less than sympathetic, and Cat gives her surprising news.
Supergirl and the DEO are called on to protect the President when she comes to National City to sign her Alien Amnesty Act. However, a hostile alien threatens to kill the President and anyone who gets in its way. Meanwhile, Alex meets Maggie Sawyer, a detective with the NCPD's science division, and Snapper challenges James' authority.
When Kara and Alex investigate the murder of an unregistered alien, the trail leads to an alien fight club run by Roulette, the ringmaster who commands aliens to fight in mortal combat for the entertainment of rich humans. While trying to stop the fighting, Supergirl and Martian Manhunter find themselves up against a surprising opponent. Meanwhile, Hank is thrilled to have found another Martian and tries to get to know M'Gann better. Supergirl takes Mon-El under her wing and begins to train him.
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