You said it.
Well, the secret's out. The clandestine project I recently completed, which is for a major intellectual property, is a Doctor Who spin-off for children.
'The Horror of Howling Hill' is another book in the 'Decide Your Destiny' range published by Penguin Character Books under the BBC Books imprint. These books, aimed at 9 - 12 year olds, send the child reader off on an adventure through space and/or time with the Doctor and his companion Martha Jones, the child deciding at the end of each page what happens next.
My own story is set in present day England, and draws on many familiar Doctor Who staples that have cropped up over the years during the original series. I had great fun writing it and got to put in all sorts of subtle - and not so subtle - references to other Who stories and SF TV shows along the way.
Check out this link to the Amazon website to keep up to date with publication dates and the like.