In Dark Phoenix, the X-men face their most formidable and powerful foe: one of their own, Jean Grey played by Sophie Turner. During a rescue mission in space, Jean is nearly killed when she is hit by a mysterious cosmic force. Once she returns home, this force not only makes her infinitely more powerful but far more unstable.

Wrestling with this entity inside her, Jean unleashes her powers in ways she can neither comprehend nor contain. With Jean spiralling out of control and hurting the ones she loves most, she begins to unravel the very fabric that holds the X-Men together.