Enid Blyton 
Go Ahead, Secret Seven [EPUB ebook] 
Secret Seven #5

With no mystery to solve the Secret Seven set themselves a few tasks. So Peter says Colin and George can do a spot of shadowing, the girls can do observations and Jack and Peter a little spying. Sadly Colin’s mother won’t let him go out so George has to do the shadowing alone. A young man watching George confronts him and takes him home, telling his parents what he was doing. Little did George know that not only would his parents stop him from being a part of the Secret Seven, but the young man in question was just the start of a mystery for the Secret Seven to solve, that included a number of missing dogs.