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 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 and ANNUAL #2, NEW MUTANTS (1983) #46, THOR (1966) #373-374 and #377-378, POWER PACK (1984) #27, DAREDEVIL (1964) #238, FANTASTIC FOUR VS. X-MEN #1-4 and X-MEN VS. AVENGERS #1-4.