Polly lives in the grounds of a stately home, Penhallow Hall, where her mother works as a museum curator and this book, The Secrets Tree, is the 4th in the series, Hounds of Penhallow Hall. The Hall is guarded by the spirits of dogs who have lived there during various historical eras, and Polly is able to ‘awaken’ these guardians and befriend them in order to together solve mysteries of the Hall’s past. I absolutely loved reading this book! I hadn’t realised it was the 4th in the series when choosing it, but the premise was explained quickly and I didn’t feel lost, and it seems each book ‘awakens’ a dog from a different time - this book looked at Charles II and the 1600s, the first at WW1 for example. It sprinkles in facts from the time period as Polly learns more about the dogs and their past owners with a heavy dose of mystery, for example in this book they needed to learn not only about highwaymen and the restoration but also how to crack codes and ciphers using different methods. A short but easy to read chapter book, I would recommend this for ages 8+ and I genuinely want to read the others in the series and find out about some of the other guardian dogs’ history and what other mysteries they and Polly can solve!