Hank McCoy sets off on his own, taking a research job but his scientific curiosity will curse him forever when an experiment gone wrong transforms him into a fanged, furry Beast. Meanwhile, the other X-Men find themselves pursued by a secret adversary that seeks to pick them off one by one. They must join forces with Captain America to save the nation and rescue their mutant comrades! Also featuring the first appearances of Wolverine and Madrox the Multiple Man, an X-Men/Avengers battle against Magneto.

Collecting AMAZING ADVENTURES (1970) #11-17; AMAZING SPIDER-MAN (1963) #92; INCREDIBLE HULK (1968) #150, #161, #172 and #180-182; MARVEL TEAM-UP (1972) #4 and #23; AVENGERS (1963) #110-111; CAPTAIN AMERICA (1968) #172-175; DEFENDERS (1972) #15-16; GIANT-SIZE FANTASTIC FOUR #4, and cover gallery for X-Men (1963) #67-93 and Uncanny X-Men (1981) Annuals #1-2.