The most brutal X-crossover of all rocks X-Factor - and forever changes Angel's life! When the savage Sabretooth and his fellow Marauders go on a killing spree targeting the Morlocks, a community of mutant outcasts living beneath the streets of Manhattan, X-Factor joins unlikely allies Power Pack and Thor to save as many lives as possible. But what terrible sacrifice will Warren Worthington III be forced to make? In the wake of tragedy, Boom-Boom returns - bringing big trouble for Beast and Iceman. Cyclops goes looking for his wife and son only to find an old enemy! And tensions will soon boil to the surface between Scott and Jean! Plus: Bobby struggles to control his powers, Apocalypse returns with three deadly Horsemen, X-Factor battles the Hulk and Scott and Jean return to the moon as the team shares an uncanny encounter with the Inhumans! Collecting: X-Factor (1986) #10-20; X-Factor Annual (1986) #2; Thor (1966) #373-374, #377-378; Power Pack (1984) #27; Incredible Hulk (1968) #336-337