One of the greatest pleasures of Doctor Who are all the aliens we get to meet - sadly all too many of them are hostile, or at least want to conquer or even destroy the earth. This book consists of two parts: firstly a listing of aliens that have appeared in the show (and some which haven't...) and secondly rules to enable you to construct your own aliens.
So, first up, Aliens and Creatures. There's a full twenty-seven of them. Some are, of course, very familiar - Daleks and Cybermen, for instance. Others may have featured far less frequently or even not at all. In each entry, there's an attempt to see what that particular alien race is like, rather than just presenting stat blocks and outlining new abilities. So there's background information about where they come from and when the Doctor has met them, notes on their motives and agendas to give you some idea about why they might show up and what they might be after, and then it gets down to detail. When they turn up, what will the party see? How will they behave and react? (The aliens, that is.) There are ideas for how to use each alien, what sort of adventures they'd be most suitable for and even a collection of plot hooks and adventure ideas to get you going. Each entry is illustrated by stills from the show.
In the second part of the book, Creating Your Own Aliens lets you do just that, providing elegant systems to enable you to let your imagination run wild, whether designing player-character aliens, traditional alien-as-villain aliens, or, well, anything else you fancy. It's done through loads of questions, by answering them you build up a clear picture of what that alien's like, then you can put appropriate numbers, traits and other game mechanics in place. Rather confusingly, all the pictures haven't been captioned, and some are for aliens not mentioned in the previous section (I spotted a Slitheen at one point...), although you don't then get notes on how to build them for yourself.
One thing that would have been useful would be a cross-reference showing which Doctor each alien has encountered, which would link in nicely with the series of Doctor Sourcebooks Cubicle 7 Entertainments have produced. There does seem to be a bit of bias towards aliens who have shown up since the reboot of the TV show, but there are some from earlier as well as ones like the Daleks who keep reappearing. However, overall there is a lot of good material here, and it will enable you to present a universe full of diverse aliens for your party to outwit in the course of their adventures.