The Hollow Man is one of the famous novels in the locked room genre. One night at the pub a mysterious stranger approaches Doctor Grimaud, and says he is his brother and threatens him.
Some days later Grimaud is waiting for a guest in the evening, and the same evening he is found agonizing in his room, and then he is dead soon after people discover him.
The main detective is dr. Fell, willing to solve the mystery of a killer who escaped from the locked room.
I honestly did not particularly like the novel, but I like the solution behind the story. The “didactic” chapter was nice: Fell teaches about locked room solutions to the other characters – but mostly to the reader.
* The Hollow Man by John Dickson Carr ★★☆☆☆½
*I read this book in italian