X-Men: Muir Island Saga

Forged from the dark parts of every human psyche, the demonic Machiavellian entity known as the Shadow King has returned! Defeated by Professor X years ago, he hungers for revenge. As Xavier‘s friends and family fall under the sway of this monstrous creature, he faces an unwinnable battle to save all he holds dear. At the mutant research facility on Muir Island, the X-Men assemble to fight alongside their mentor once again… but could it be for the final time? Collecting Uncanny X-Men #278-280 and X-Factor #69-70.