Fiction by Ruth Ware.
In this story, a woman goes on aan ocean cruise and may or may not hear a body being thrown overboard in the middle of the night.
It's a good thriller; it's got a great beginning and a great end but it drags just a bit in the middle. (I say that to clarify the difference between a good thriller and a great thriller.)
I'd recommend it for the plot surprises.
I also read by this author: In a Dark Dark Wood