Grandfather boots the kids out of the house for another trip, sending them on a cycling holiday to their aunt's house. On the way they find a lost dog, and the rest of the trip is dedicated to finding the dog's owner and returning him to them. Of course they succeed, but I enjoyed that for once - criminal lurkings in the background aside - in this case the dog really was lost, which is a very mild mystery but also an understandable one. Far more mysterious is four children volunteering to do a stranger's housework, which I suspect is meant to come across as kindness and goodwill to all, but which skirts the line of mildly disturbing. (Next stop Stepford, perhaps?)