Nicholas Blake 
Whisper in the Gloom [EPUB ebook] 

A VINTAGE MURDER MYSTERYA small boy playing in the park is handed a crumpled piece of paper by a stranger, who then collapses and dies. The boy, realising that he himself is now in danger, flees from the park with the help of detective Nigel Strangeways, only to discover that the mysterious message consists of just his own name and age: Bert Hale 12. Bert and his young friends are confident that they can crack the case but they soon discover that they will need the help of not just Nigel Strangeways, but of the whole British government…A Nigel Strangeways murder mystery – the perfect introduction to the most charming and erudite detective in Golden Age crime fiction.