Time Cat

A children's novel written by Lloyd Alexander and published in 1963.

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.

Tropes used in Time Cat include:

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.
Bittersweet Ending
Cats Are Magic: Cats can talk and transport themselves anywhere in space or time that they choose.
Cute Kitten: Everyone falls in love with the Manx cat's kittens.
Fish Out of Temporal Water
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.
The Gump: 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.
Historical In-Joke
Intellectual Animal: What Gareth becomes to Jason after their trips through time are over.
Kindhearted Cat Lover
Lighter and Softer: Understandably, since it's a children's novel published in the early sixties. Many historical conflicts are implied to have been concluded without bloodshed.
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.
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.
Stable Time Loop
Talking Animal: Gareth.
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.