Storm, Sprite, and Spider-Woman try to enjoy a night out together when a mysterious new mutant crashes the party. Meanwhile, the shipwrecked Cyclops and Lee Forrester explore a strange island that appeared out of nowhere.
Professor X charges the X-Men, returned from space, with reconnaissance of Muir Island and its inhabitants, while he tends to things back in New York. Unfortunately this plays right into the hands of their unseen adversary: The Shadow King!!
With the Uncanny X-Men out of contact on Muir Island, Professor X turns to the only people he can trust: his first students and original X-Men- X-Factor! Will this happiest of reunions under the most dire of situations be enough to overcome the Shadow King??
The final battle between Xavier and the Shadow King takes place on the astral plane as X-Man battles X-Man all around them. The Muir Island Saga reaches is conclusion and the X-Teams are changed forever!!