X-Men: Dark Mirror by Marjorie M. Liu
In the fourth instalment of Pocket's new series of Marvel novels the mutant superhero team could be the future's only hope. Jean Grey awakens in an unfamiliar room. She is weak, disoriented, stripped of her telepathic and telekinetic powers- and trapped in someone else's body. Also prisoner are her teammates Cyclops, Wolverine, Rogue, and Nightcrawler- each of their minds held hostage within the bodies of strangers as well. Who has brought them here, and for what purpose? The answers lead to a terrifying plan that threatens not only the X-Men, but all of mutant-kind.