While Tarzan, Jane, Archimedes Q. Porter and Samuel T. Philander are in Pellucidar, they discover a Tyrannosaurus nest. In order to have a proof that dinosaurs are still alive, Professor Porter secretly steals an egg, but soon after the group leaves the mother Tyrannosaurus arrives and sees that one of his eggs is missing. She rapidly finds the group and attacks it, but they flee and take refuge in a huge trunk. Here, the egg hatches and a baby tyrannosaurus gets out from it. Tarzan manages to exit from the trunk and distracts the Female Tyrannosaurus, allowing the others to escape. Pursued by the dinosaur, Tarzan swings on vines and succeeds to use one to tie her to a tree's branches. However, she quickly frees herself by snatching the branches and one of it falls on Tarzan, immobilizing him. Jane comes to help him, but the Female Tyrannosaurus approaches. Just before she devours them, Professor Porter comes and gives her the baby. Although happy to recover her progeny, the Female Tyrannosaurus still attacks the group and pursues it. Samuel T. Philander climbs the rope with which the group went to Pellucidar and orders to his henchmen to withdraw it, abandoning the others. As the Female Tyrannosaurus is about to catch them, Professor Porter gets the idea to use methane gas to propel a tyrannosaurus's skull upwards. After the group climbed on the skull, the Female Tyrannosaurus attempts to devour them but Professor Porter ignites the gas with his flashlight, projecting the skull beyond Pellucidar.