Only Human by Gareth Roberts
A good short read for an afternoon or a great book for kids, this Doctor Who story goes right back to series one and features Rose, Christopher Ecclestone's Doctor and Captain Jack.
We open with a strange diary entry from 7 year old Chantal in the year 438,533. Humans are obviously still around, but language has shifted. Chantal speaks of 'wrong-feelings' and genetically re-engineering her cat.
From this unsettling entry we are hurtled into far more familiar territory, the carnage of people in fancy dress in a present day nightclub, a brawl begun over one bloke looking at another's girlfriend the wrong way and the thug who bites off more than he can chew when he picks a fight with a caveman. Except this one really is a caveman, well, a Neanderthal to be precise, a long long way from his own time.
Cue the TARDIS, and Rose, the Doctor and Jack just about to go on holiday to Kegron Pluva when a flashing warning light indicates a temporal disturbance and, as usual, the holiday is derailed for high adventure in 2005AD and 29,185BC involving Neanderthals, Homo Sapiens, humans from the 437th century and some lethal genetic engineering. The very best of Doctor Who, excellent witty characterisation and great imagination.