This is a really nice, if rather formulaic, children’s adventure/mystery book, published in 1950. Some baddies have stolen a load of treasure. Our heroine Alison and her brother Niall, during their holidays from boarding school, uncover the baddies’ identities and find where the treasure’s hidden, beating the authorities to it. There’s someone in disguise, and an old house with a hidden passage, and various mysterious goings-on – because, if you were snooping round a house, obviously you’d help yourself to a load of chocolates from an open box and make it really obvious that someone had been there!
You get the idea. But it’s a lovely book. It’s set in the Scottish Highlands. There’s a lot of reference to wearing kilts, and everyone goes fishing and plays golf all the time. The authorities are represented by the children’s uncle/guardian, so they’re all on friendly terms and there’s no sneering at the police. There’s a lot of dashing about in cars and boats, but nothing completely unrealistic – Ruritanian princes being sacrificed to sun gods, that kind of thing 😉 – happens. It’s just a nice old-style children’s book, and it holds up very well over 70 years after it was published.