The Labyrinth of Time
The book is full of ideas about time, starting with what philosophers have had to say on the subject, and moving on to the nature of time in relativity, thermodynamics and quantum theory, as well as considering the possibilities of time travel.
One thing I wasn't too keen on was the derivation of the deterministic 'Block Universe' view from special relativity, a derivation which I think is philosophical sleight of hand. This doesn't detract from the rest of the book, although as I was reading I did begin to wonder about the lack of any discussion of Deutsch's many-worlds ideas of time travel, which was conspicuous by it's absence. It turned out that Lockwood was leaving it until last, as the method of time-travel which he thought of as most likely to be possible.