Day Four (The Three #2) by Sarah Lotz

Four planes. Three survivors. One message. It seemed like the end of the world... but it wasn't. This, however, just might be.

The extraordinary, unforgettable sequel to THE THREE - perfect for fans of The Shining Girls, The Passage and Lost.

Four days into a five day singles cruise on the Gulf of Mexico, the ageing ship Beautiful Dreamer stops dead in the water. With no electricity and no cellular signals, the passengers and crew have no way to call for help. But everyone is certain that rescue teams will come looking for them soon. All they have to do is wait.

That is, until the toilets stop working and the food begins to run out. When the body of a woman is discovered in her cabin the passengers start to panic. There's a murderer on board the Beautiful Dreamer... and maybe something worse.