The Woman in Cabin Ten by Ruth Ware

Lo has the bad fortune of being burglarized right before she is due to cover a luxury cruise to the Fjords.  Still jumpy to say the least she does not sleep well, even on those 1000 count sheets, and wakes to the sound of something or someone being dumped overboard.  Then, when no one is missing and there is no evidence to prove her case, she begins to see threats telling her to lay off.  Not knowing who she can trust from her colleagues to cruise staff does not help the situation.  Deliciously twisted plot lets you wonder right along with her if she did witness something and if she will survive the cruise to tell anyone about it.  The ocean is cold and deep and she is far away from help.  This summer's "Gone Girl on a Boat" will have people talking.