Every now and then we come across a MG mystery that breaks the "rules" of writing for this age group, and this one does it deliciously!
First of all, people die. Gruesomely. It's a three-body murder mystery, with a mad professor who experimented on children. It's got a shrunken head, containers of cyanide lying 'round the house, and all sorts of 19th century grotesque curiosities.
Secondly, the four children investigators (each with their own mysterious "power") pursue the mystery to all sorts of forbidden places - including the inside of the chilled drawers in the morgue!
Well plotted, and we loved the cast of characters. Simply wonderful.