I don't know what age range these books are aimed at, and I don't care. I'm 41 and I loved it. This one (fairly obviously) is a Hitchcock pastiche. Alright, a lot of the jokes are corny. That doesn't stop them being extremely funny.
This time, Tim and Nick Diamond are on the trail of a ruthless killer while on the run from the police. Yes it has a scene in a cornfield. Yes it has Rushmore (read it to find out). It has many more references. And it has the famous Diamond Brothers.
More please Mr Horowitz!