In a world where men can turn into monsters, one girl must sacrifice everything to save the one she loves.

In the city of Galex, all that matters is your genetics. Living with a virus that only affects the male Y chromosome, men Ys are at risk of death or mutation and are treated like slaves, considered too dangerous to live freely. Women Xs- rule the city.

Cara must navigate a world where the one she loves is considered a deadly enemy. With her sister Myla in charge of Galex and driven by a hatred of the Ys, Cara has a dangerous secret. If discovered, it will not only destroy her relationship with her sister, but will threaten the life of the Y she loves.

Brown has spent his life enslaved, knowing he could mutate at any moment. After seeing his best friend killed, he volunteers for a deadly mission. He is soon to face a difficult decision: protect Cara and sacrifice her sister, or betray his fellow Ys and place all his loyalty in the hands of an X.