This book is created from a series of lectures that the author gave to teenage schoolchildren. As such it is entirely non-technical, but succeeds very well in linking the science of the theory of relativity with sci-fi concepts such as wormholes and time travel. It also includes an introduction to cosmology and a discussion of the philosophy of time. I would recommend it to any reader wanting a gentle introduction to these subjects or to more advanced readers who will enjoy it as a little light reading.
The book is in three parts, on Space, Time and Time machines. The first part looks at curvature of space and so introduces Einstein's general theory of relativity. The second part examines some of the philosophical issues concerning time, and then goes on to the Special theory of relativity. This means that GR is dealt with before SR, which reverses the order in which they were developed, but this doesn't seem to cause any problems. More puzzling is the chapter on time travel paradoxes in part 2 rather than part 3. I would have thought this chapter would be better after the description of how a time machine might be built, and in particular the self-consistency argument for 'wormhole billiards' would make more sense.