A Tale of Time City is essentially what it says on the tin: a tale of Time City, a fantastical city built on a loose fragment of time and space which stands outside of human history. Its inhabitants, much like Terry Pratchett's History Monks, look after the progression of events in history so that it doesn't get mucked up, essentially. But - dun dun DUN - the end of Time is coming, and someone's stealing the Caskets that will ensure the continuation of the City. So a couple of Time City children kidnap London girl Vivian Smith from an evacuee train in 1939, believing that she can help them, for reasons that never really become clear.
So A Tale of Time City is kind of hard to evaluate. I'm not even quite sure what genre to call it: the time travel stuff is classic SF, but the book feels very fantastical, full of objects like the Caskets and their guardians which clearly have their roots in classic fantasy, as well as time-ghosts, glass clocks and libraries which break the laws of physics. As concepts, they're all pretty cool, actually; I especially enjoyed the idea of time as a horseshoe which rotates endlessly, and the need to renew Time City once every cycle.
I personally found the book quite hard to get into, though, possibly because the voice is fairly dated (originally written in 1987, so understandable, I suppose), but also because there's such a swirling mix of seemingly interchangeable names and reference points that it's difficult to work out precisely what is happening where and when and why. The time travel doesn't help particularly.
Also I was kind of horrified by the scene in which Vivian effectively force-feeds one of her friends as payback for a prank. I don't know if this is supposed to demonstrate that Vivian is not a goody-two-shoes or a Mary Sue or whatever, but it comes across as really quite violent and unnecessary.
Three stars, anyway, for originality and imaginativeness.