One might expect a book called Travels in four dimensions: The enigmas of space and time
to be primarily concerned with the theory of relativity. Einstein does get a look in in Robin Le Poidevin's book, but it is more concerned with other aspects of the philosophy of time. The book is in the science section of my local library, but I feel that it is more of a philosophy book, and that the 'popular science' bits - time travel, multiple universes and the like - are the weakest parts of the book. But what it does well is to introduce the reader to philosophical ideas about time in a clear and readable way. If you've read popular science books about time, but would like to hear more about what philosophers have had to say on the subject then you should give this book a try.
The book starts by looking at whether time is anything more than things changing, and at Newton and Leibniz's ideas on absolute and relative space and time. Le Poidevin then considers the nature of the universe - the big bang, non-euclidean geometry and whether the universe is infinite. He then moves on to look at Zeno's paradoxes and McTaggart's ideas of A and B series. The last part of the book is more 'popular science' in nature (which as I have said I wasn't that impressed with), looking at time travel, parallel universes and the different arrows of time.