The After House (Unabridged‪)‬

Fresh out of the hospital and low on funds, a young doctor decides to take a long sea voyage to restore his health. He signs on as a steward on board a millionaire's yacht. Then, one hot and humid summer night, the voyage starts to become a nightmare.
One of the ship's officers is thrown overboard. Another one is killed with an axe. The killer strikes again and again, and the rest of the passengers begin to panic. Only the young doctor remains calm and tries to solve the murders, but to do that he will have to stay alive, something that won't be easy.

Here is another classic from the Mary Roberts Rinehart, a master of mystery and suspense.