Thunderbird coordinates a mission to discover what Sentinel Services had done to an old friend of his and Lauren encounters a new friend with useful powers.

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.

The Inner Circle prepares for a secret ambush, but Polaris is reluctant to join and Reeva tasks Esme with getting Polaris on board. Esme confides in Polaris, revealing her and her sisters' troublesome past. Meanwhile, Thunderbird trains Reed on controlling his powers and The Purifiers attack The Mutant Underground as they attempt to rescue a group of homeless mutants.