Warren dies and is resurrected by the strange "Creator", who is at war with Ka-Zar. The Creator has put together a team of mutants from the Savage Land population - Amphibius, Barbarus, Equilibrius, Piper, Lorelei and Lupo. It's a bit of an odd name for a leader, and he's soon revealed to have not just recruited these people (not actually called the "Savage Land Mutates" in the text yet) but artificially induced their mutation in the first place.
In one of those deft masterstrokes that you can only pull off once, he's then revealed to be Magneto, adopting the cunning disguise of not wearing a red-and-purple costume or helmet. This is the second time Magneto's been creating a mutant army, rather than seeking to lead existing mutants (after X-Men #17-#18, where he creates them ex nihilo). Warren thought he was dead after the events of the crossover with Avengers, which is a bit surprising, as I don't see how Warren could have known that the Magneto he saw in #49-#53 was a robot. After that it's your basic fighting thing, albeit with a new cast of mutants to play around with. There's a clever (if mildly sexist) bit where Lorelei mesmerises the boys, but Jean is left unaffected, and is able to use her TK to trigger Cyclops's visor. They win, of course. They leave Magneto for dead, in a burning building. So much for "X-Men don't kill", which seems to be born mostly out of the fact that the people they were happy to leave for dead always miraculously survived, rather than some moral rule.