Ngaio Marsh 
Singing in the Shrouds [EPUB ebook] 

With this novel of mounting tension among apparently normal people, Ngaio Marsh achieved a triumph on a level with her most famous detective novels Surfeit of Lampreys, Scales of Justice and Off With His Head.On a cold February night the police find the third corpse on the quayside in the Pool of London, her body covered with flower petals and pearls. The killer walked away, singing.When the cargo ship, Cape Farewell, sets sail, she carries nine passengers, one of whom is known to be the murderer. Which is why Superintendent Roderick Alleyn joins the ship at Portsmouth on the most difficult assignment of his professional career…