The blurb goes on about it being passionate and bubbly and whatever, but don't be put off.. it really is good! It's a rare example of a science book which is hard to put down in the way a 'good read' should be, but is more informative than many pop science books come near.
In brief the book covers what he looked for (identifiable patterns in mitochondrial DNA); what he found (they exist, and are special because they only pass from mother to child); and what that means (he could prove not only that we're all related but how, when and where). He talks about his excitement at the 'we're all related' factor, and although I started out cynical, or rather apathetic, I was excited too by the end of the book. If you're a 'Helena', then you descend from the same great.... grandmother as anyone else with that marker, which could be your bloke, your dad (as well as your mum), your girlfriend, the bloke selling the big issue on the corner, the confused-looking people on the telly in some Baghdad hospital... when you start thinking about the implications, it gives you a rather funny feeling, and that is what Sykes says is the whole point of the work he does.
And even if fluffy we-are-all-one feelings are not for you, I bet you'd be fascinated by the information the book contains!
Oh - and as a painless primer in pre-history it's not half bad either.