Eclipse's ex-lover returns; Reed and Sage find alarming information about Lauren's new friend; Thunderbird helps Blink open up about her past; Jace approves a special surveillance program.

Polaris learns more about her past and makes a crucial decision that could have impactful consequences. Meanwhile, the Mutant HQ comes under attack and, with everything to lose, relationships are put to the test and alliances shift.

When one of the Inner Circle goes missing, Reeva intensifies security in their compound, but realizes that her plans may have already been exposed. Furious and paranoid, Reeva resorts to violence. Caitlin and Reed consider using the serum to restrict Lauren's use of her powers, hoping it will help her as she wrestles with nightmares about the Inner Circle and her ancestors. And it's the battle of two extreme ideologies when the Morlocks and the Purifiers come face-to-face in battle.