Joshua Foley was raised to hate mutants, but when his healing powers manifested, the violent anti-Mutant Reavers rejected him and only the X-Men offered sanctuary. His anti-Mutant upbringing puts him at odds with the other X-Men, but things get even more challenging when sea monster-worshiping vampire mermen attack the remote underwater station where he and a select team of new X-Men are on a deep-sea training mission. Then, they find themselves in an even more dangerous situation when it becomes clear that an ancient leviathan is sealed beneath the ocean floor, and it's about to awaken.