The Juggernaut, courtesy of a ruse engineered by Black Tom Cassidy, allies with and joins the X-Men; the plan is to destroy the team from within. When Cassidy openly betrays the Juggernaut, Marko attempts to change his ways and joins the X-Men. The Juggernaut befriends a young mutant boy called Sammy Paré, who helps Marko reform, despite setbacks such as a battle with the Canadian superhero team Alpha Flight. However, when Paré discovers that Exodus' Brotherhood of Mutants is preparing to attack the X-Men's headquarters while unaware that Juggernaut is the mole in their group, he is killed by Black Tom Cassidy. An enraged Juggernaut attacks Cassidy and his allies, and the battle strands all participants in the Mojoverse.