It's fast-moving and funny and a clear case of a writer wanting modern kids to be able to enjoy the kind of adventure he got to read as a child. There are a lot of them now. There's plenty to be said for those old adventure stories, so if current writers can do them too, good on them.
I'm still two-thirds of the way through, so I'll keep the main comments for the review, but so far - what a hoot! Villains, kids running around trying to find a stolen diamond, the boy who's suddenly the richest kid in the world and finding himself a target for murder. Can he and his friends find the missing treasure? Can he solve the mystery before the villains succeed in killing him?
I'm betting the answer to those questions is yes! It always was in Enid Blyton. But then, Julian, Ann, Dick, George and Timmy the dog were never in any real danger, were they? Not in the books I remember reading.
I can't wait to read the sequel, which is waiting on my to-be-read pile.