The Doctor Who books (new 2005 series) are all short but very sweet. They are pretty simple, but I love how they convey the same humor and feelings that a traditional Doctor Who tv episode does. The books I have read so far all had that same great humor by the Doctor that I love, which is why these books are almost like comfort food for me.
In this book the Doctor (9th) and Rose find a genuine Neanderthal in the UK, in Bromley, in the twenty-first century. When they find out how he got there, they discover a colony of future humans living in 26.000 BC. They are using a crude time-travel device, and the Doctor needs to figure out what they are doing there and stop them using the device again. Meanwhile, there is also the problem of the Neaderthal to think of.
Like I said, a great short book, truly Doctor Who.