Peter's dog Nell has an amazing sense of smell. Whether it's finding a lost shoe or discovering who did a poo on the new gravel path, her ever-sniffing nose is always hard at work. So who better to have on hand when the children arrive one morning to discover that the school's library has been plundered? Who could have taken the books, and why? There's only one dog for the job, and Detective Dog Nell is ready to sniff out the culprit.