The first X-Men crossover event -- and still the most brutal! When Sabretooth and the lethal Marauders attack the underground outcasts known as the Morlocks, the X-Men, X-Factor and New Mutants join forces to stop them -- with help from Thor, Daredevil and Power Pack! But the cost of victory is very high, and many X-Men come away badly injured. While Shadowcat might be saved with the Fantastic Four's help, the Angel contemplates a much bleaker fate! Psylocke, Longshot and Dazzler join the undermanned X-Men -- just in time to clash with the Avengers -- as Marvel's mutants struggle to recover and rebuild! COLLECTING: Uncanny X-Men (1981) 210-219; X-Men Annual (1970) 11; X-Factor (1986) 9-17; X-Factor Annual (1986) 2; New Mutants (1983) 46; Thor (1966) 373-374, 377-378; Power Pack (1984) 27; Daredevil (1964) 238; Fantastic Four vs. the X-Men (1987) 1-4; X-Men vs. the Avengers (1987) 1-4