Why is the X-Men's newest crisis shaping up to be... their final adventure?! It all starts with a mysterious and tragic disappearance, but their investigation draws the X-Men into a much larger -- and deadlier -- situation! Who or what are the Four Horsemen of Salvation, and what is their connection to Nate Grey, the incredibly powerful mutant known as X-Man? Will Nate's home dimension, the Age of Apocalypse, make its horrifying return? Or does the dawn of the Age of X-Man mean the end of the Uncanny X-Men?!