The sole season of the show comprised four serials; the first two, and the last, were 6 episodes long, whilst the third ran to 8 episodes. A second season was mooted, but was clobbered by several different factors, including the production running wildly over-budget, and industrial action by technicians meaning that several episodes were produced in black-and-white, which badly affected overseas sales. All 26 episodes still survive, although only one of them in a colour format, and the series remains fondly remembered to this day.
In 2019, Big Finish announced they would be releasing a new audio series featuring original cast members Banks and Burfield, continuing the story 50 years later.
This series provides examples of:
- Adaptation Expansion: Like many other British series of the time, there was a tie-in comic strip, which was published in Look-In. The series was so popular that the comic kept on going for a full two years after the series ended, with the editors of Look-In trying on more than one occasion to quietly phase it out only to encounter resistance from readers.
- Exty Years from Publication: Originally broadcast (and set) in 1970, the first serial saw the characters travelling back to 1940, and later serials showcased two different alternate versions of 1990.
- Randomly Reversed Letters: The series' logo variously appears with the two 'I's upside-down and/or back-to-front, with different orientations appearing in the opening credits, ad bumpers, end credits and merchandise. They even re-filmed the opening credits, and still didn't manage to get it right on the second attempt!
- Time Travel: Simon and Liz can travel to different time periods and alternate futures.
