The Challs guard a recently unearthed sarcophagus but a harpy creature breaks in and steals it. Arriving at Skull Island the heroes find an underground lab of extinct creatures. They fight back but are gassed. They awaken in new uniforms with hourglass emblems facing a council of scientists mutated by radiation. The Challs are asked to mutate but refuse; in order to free his friends Prof subjects himself to the transformation. His mind is affected and he attacks the Challs. When the transformer blows up Prof reverts to normal. The explosion destroys the island as the team escape in their jet.; The Challengers are transported to Challenger Mountain in the year 2265 where the Godzilla-like Monstro, is ravaging domed cities. Monstro was shot to Earth in 1900, hatched in 1965, bored to the Earth's core to incubate, and returned to the surface in 2265. The Challengers must kill Monstro in 1965. Returned to their own time, the heroes don asbestos suits and follow the egg into the Earth. Baby Monstro emerges, but grenades can't kill it, and the monster bores deeper where it's too hot to go.