When a man needs a costume for a masquerade party but all the shops are closed, he finds a lion skin in an antique shop to use as a Hercules costume. But what he doesn't know is that the lion skin really did belong to Hercules, and that it grants the demi-god's strength to whoever wears it.
Colin was Earth's top test pilot, checking out special purpose ships, until the day it appeared that he and his partner had turned in a false report. Unable to find work again on Earth, he ends up testing ships for an alien race.
After two anthropologists bring an Amazonian caveman back to the states, he begins to progress at a rapid rate until his intelligence and appearance jump beyond where modern-day man is on the evolutionary path.