The novel starts off with the protagonist, Jason, a boy who is having a bad day. His black cat, Gareth, enlightens him to the fact that cats have magical qualities that allow them to speak and travel through space and time at will. Together, Jason and Gareth travel through various periods and locations throughout history on a series of adventures involving cats.
This novel provides examples of the following tropes:
- Battle Discretion Shot: A lot of the historical events in Time Cat are known to have ended less than peaceably, and Gareth and Jason conveniently skip out of time for a lot of them.
- Beat Them at Their Own Game: Gareth and Jason ensure that a witch-hunter is himself accused of magic.
- Been There, Shaped History: Jason ends up being a part of many historical events and meeting and influencing various famous figures from the past during his adventures with Gareth.
- Cats Are Magic: Cats can talk and transport themselves anywhere in space or time that they choose.
- A Child Shall Lead Them: When Jason and Gareth travel to 10th century Japan, they meet Emperor Ichigo, who's barely older than Jason himself.
- Cute Kitten: Everyone falls in love with the Manx cat's kittens.
- Forgot About His Powers: Jason and Gareth are often captured and held somewhere against their will. Despite having the power to travel to any point in space or time, Gareth never uses his magic to allow them to both escape. Justified in that he only has nine goes, and so presumably doesn't want to use the abilities more than necessary.
- The Masquerade: Cats can talk, travel through the space-time continuum at will, and perform all sorts of secondary magics, but keep it a complete secret from humans.
- Mundane Utility: In general, cats use their Hiro power to get out of locked rooms and other places they find unpleasant.
- Not So Stoic: Gareth is an old school sort of teacher to Jason; focused, no-nonsense, a little aloof. He also takes a quick break to impregnate a wildcat.
- Or Was It a Dream?: After their adventures, Jason wakes up at home from a nap to an unspeaking Gareth. But still has an ankh that he kept from when the two were in ancient Egypt.
- Translator Microbes: Gareth's magic allows Jason to understand and speak the common language of whatever place and time period he's in.
- A Wizard Did It: Gareth's power, which allows Jason to blend in to his temporal and cultural surroundings nearly seamlessly. It gives him Translator Microbes, adapts his clothes to current fashions and presumably keeps him from contracting common pathogens of the times and dying before he gets back.
- Year Inside, Hour Outside: Many of the trips occur over several days or even months, but once it's over only half an hour has passed in the present.