The plot setup was based on the concept of an experimental time machine that has sent two people back in time -- but cannot retrieve them. The time travellers are swung from one period in history to another, allowing episodes to be set in the past and future. Many episodes reused sets created for other Irwin Allen television and movie productions. The plots were not noted for historical accuracy.
Only one series was made, originally airing in the 1966/1967 season.
The principal characters were: