Scientist Captain Z-Ro, working in his remote laboratory, safeguarded mankind and history from impending harm. He had a time machine, the ZX-99, both to view history and to send someone back in time. Each week, he and his teenage assistant Jet would view an episode in time and inevitably see that some event was unfolding contrary to history (e.g., King John not signing the Magna Carta). Captain Z-Ro would then send Jet back in time to intervene and ensure that history played out as originally recorded. Over the years, plots involved Z-Ro and Jet rescuing a wide range of historical figures, including Genghis Khan, Marco Polo, Magellan, William the Conqueror, Benedict Arnold, William Tell, Christopher Columbus, Blackbeard, Captain Cook, Leonardo da Vinci, Robin Hood, George Washington, Attila the Hun, Hernando Cortez and Daniel Boone.