In this book Holly, Tracy, and Belinda, aka The Mystery Club, travel to London for a visit, and an adventure, with Miranda and Peter, Holly's friends from an earlier series, The Mystery Kids. I love this series and this was a great book, but I didn't like it as much as the others. No distinct reason why....
It all starts when Holly, Tracy, and Belinda accompany Miranda on a babysitting job to an actress's home to stay with 5 year-old Charlotte. They meet Gail, a woman who has just moved in with Suzanne and Charlotte. Charlotte doesn't like Gail and the girls also become suspicious of her. Charlotte is quite capable of innocently diverting contraband that not only Gail wants, but also some other dangerous people are after. It's a mad race to get to it all before the other factions do, and the climax unfolds in the theater high above the stage during a performance.