The "Muir Island Saga" is a five-part Marvel Comics crossover event involving the X-Men and X-Factor, published in 1991. It was written by Chris Claremont and Fabian Nicieza.

After warnings from Forge and Banshee, the X-Men and Professor X investigate Muir Island, whose inhabitants have been taken over by the Shadow King. They are captured by the inhabitants. Professor X returns to his mansion, now in ruins after the Inferno storyline, to use Cerebro, only to find Stevie Hunter on the run from Colossus, also controlled by the Shadow King. Professor X battles Colossus and frees him from the Shadow King's control, but he is forced to strip away the Peter Nicholas persona he had been using since passing through the Siege Perilous. Xavier decides to call in his original students, now forming the team X-Factor.

On Muir Island, Wolverine separates himself from his party and is attacked and freed from control by Forge. Rogue appears, ready to attack, but she too is taken out by Forge. The three regroup, but are quickly attacked by Banshee, who is also quickly taken down and freed. Banshee explains that Shadow King has been using Polaris as a nexus between the physical world and the Astral Plane since the time Zaladane stripped Polaris of her magnetism powers. Using her new powers to absorb negative energy for superhuman strength, Shadow King plans on becoming all-powerful. They fear that to break that connection and defeat him, they may have to kill Polaris.

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