I don't think there was much of a way I could go wrong here. Two of my favourite authors collaborating on a book. Well, okay I am biased but this is what I like about SF. Asimov's short story about a Neanderthal boy brought forward in time as part of a science experiment expanded to novel length is a superb story. My worries over the padding that might have been required to do this were groundless, this reads like it was always meant to be a novel.

On this kind of standard it is a shame there are only three of these collaborations.