Enid Blytons The Mystery of the Secret Room is the third book in the 5 Find Outers and Dog series. Im reading the series as part of a readathon. It wasnt the best book of the series so far, certainly it doesnt have the surprising detail in characterisation of The Mystery of the Disappearing Cat. It also takes a while to get going, but it reads very quickly once it does. Perhaps if this had been a Barney mystery, things would have been fleshed out more, but it seems that the 5 Find Outers are more case focused, junior versions of Sherlock Holmes, rather than simply children who randomly fall into adventure during their school holidays.