In 1929 the fossil of a 500,000 year old man is discovered in China. In 1941 the Japanese army confiscates this find, but during the war the remains disappear. Based on these factual events, this movie takes off with a science fiction story involving a space rocket which places a satellite in orbit containing a secret cargo. The satellite crashes on a remote island and footprints are found in the sand leading away from the crash site. A story of how an ancient primitive cave-dwelling family contends with the scientists who want to study them.

When the Shogunates greatest secret is stolen, the fate of the nation hangs in the balance. The Shogunate sends an incompetent cop, Tanaka, to Kyoto to act as a stalking horse. Hoping the thieves will kill Tanaka and the Ninja Spies will kill the thieves. But what the Shogunate doesn't realise is that Tanaka's even more incompetent assistant Mondo is in fact the leader of a gang of revengers for hire, there motto is "Sure Death" (or your money cheerfully refunded). Mondo doesn't know that everyone knows about the secret, but they all think he does. Poor Mondo, he not only has to deal with crazed Shogunate extremists, oddball ninjas, crooks who work for the Emperor and bicycle riding foreign death squads. He also have to deal with a wife and a crazy mother-in-law!