The mystery in the garden

Nancy and Dom's photographer father is going to the Antarctic to hang out with seals. Nancy and Dom are not. They're going to stay with the eccentric Miss Heatherbell and her hordes of free-range guinea pigs, which doesn't seem quite as exciting as meeting an elephant seal named Brian. But Miss Heatherbell's house is large and mysterious, full of surprising rooms and odd objects. And it looks like something is hiding at the bottom of her enormous...