Practising their powers in the Danger Room the other X-Men wonder why Angel is late for training. They check his room and find him in front of his TV where he is watching a video footage about an incident that happened during an Antarctica expedition. One missing person of the crew had been rescued by a wild man accompanied by a sabertooth tiger.
The X-Men discuss who that man might be and how he can survive in that cold environment without any protective clothing. Thinking him to be a mutant, they suggest to investigate Antarctica to Professor X. Since the X-Men have been inactive for weeks, Xavier gives the mission his OK, even though his mental probes revealed that the wild man is not a mutant.
Days later the X-Men have traveled to Antarctica and they are starting to search for the wild man at the spot where he was last seen. They find a very deep crevasse and a hidden tunnel through which the wild man must have escaped. After hours of descending into the tunnel they emerge in a gigantic cave and Angel is attacked by Pterodactyls. After outmanoeuvering most of them and some blasts from Cyclops, the Pterodactyls go away, leaving the team to check their new surroundings.
The cave, even though being in Antarctica has a warm tropical climate and all plants and animals are prehistoric. After the Angel takes off to scout the terrain, his teammates are suddenly under attack by some savages riding dinosaurs. Using grenades filled with volcano gases, they render all but the Beast uncosnscious and surely they would have defeated Hank too if not for the timely interference of Ka-Zar and his pet sabretooth Zabu.
The savages ride away on their dinosaurs but take Marvel Girl with them. Fearing for Jean’s safety, the tempers of the X-Men flare, which Zabu perceives as an attack on his master. A fight starts between Ka-Zar and the mutants, but it is interrupted by Ka-Zar’s archenemy Maa-Gor of the Man-Ape tribe. Ka-Zar defeats the primitive alone and the incident showed him that he and the X-Men have common enemies; he decides to help the X-Men in retriving their teammate.
Meanwhile the Angel is still on his scouting mission and is impressed by the various dinosaurs that live in the Savage Land when suddenly a net is thrown on him. Caught and outnumbered, the Angel is tied up and taken into the city of the swamp men where he is brought to Jean who is also tied up. Marvel Girl tells Warren that the savages intend to sacrifice them and that she is unable to free herself since her ropes are covered with pitch.
The two mutants are brought on top of a small hill and suddenly a door opens from which a tyrannosaurus rex emerges. Jean uses her power to toss some rocks at the creature and pulls on one of its legs to make it topple; this gives her enough time to concentrate on Angels ropes that have not been treated with tar.
Free to go, Angel grabs Jean and takes off, but his wings are still cramped from being tied up. He can’t fly high enough with carrying his passenger and the swamp men pull both him and Jean down again.
Ka-Zar and the other X-Men arrive. The wild man calls up a herd of mastodons that deals with the outer perimeters of the swamp men city. Once inside the mutants have the element of surprise on their side and they can easily rescue both Warren and Jean.
Ka-Zar leads the X-Men back to the hidden tunnel to Antarctica. Cyclops wants to thank their newly made friend but Ka-Zar as Lord of the Jungle orders them to leave and never return.
After they left he again calls the herd of mastodons to seal the hidden tunnel with tons of crashing boulders.