The first X-Men crossover event -- and still the most brutal! When Sabretooth and the Marauders attack the underground outcasts called the Morlocks, the X-Men, X-Factor and the 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. THE X-MEN #1-4 and X-MEN VS. THE AVENGERS #1-4.