During a daring rescue mission in space, the X-Men face a powerful cosmic force that nearly kills them. Jean Grey, one of the team's members, absorbs a massive amount of energy, saving the mission but altering her in unpredictable and potentially destructive ways. Jean's powers are drastically enhanced to the point where she can neither comprehend nor control them. As she struggles to cope with her newfound abilities, which seem to amplify her emotions and memories, her pain and confusion unleash chaos around her. The incident begins to tear the X-Men family apart, as they try to understand what is happening to Jean and to protect her from the consequences of her increasingly unstable powers.

The X-Men's internal struggle coincides with external pressures, as the team faces escalating anti-mutant sentiment from the government and public. This tension exacerbates the rift within the group as they grapple with the moral implications of Jean's transformation and the potential threat she poses. Meanwhile, Jean's quest for self-discovery and control leads her down a dark path, as she encounters mysterious new figures who have their own interest in her abilities. Her relationships with the X-Men, especially those she's closest to, become strained as she oscillates between moments of lucidity and outbursts of destructive force, challenging the very ideals the X-Men stand for.