The Last One by Will Dean

This book is intense, exciting, and full of action and plot twists. The writing is smooth and flows easily from one scene to the next. The main character has a complicated past that adds a level of mistrust to everyone she meets and is explained gradually throughout the book. There's an underlying sense of doom, especially the first half of the book, that adds tension to the whole story. 

From the book description:

When Caz steps onboard the exclusive cruise liner RMS Atlantica, it’s the start of a vacation of a lifetime with her new love, Pete. On their first night they explore the ship, eat, dance, make friends, but when Caz wakes the next morning, Pete is missing.

And when she walks out into the corridor, all the cabin doors are open. To her horror, she soon realizes that the ship is completely empty. No passengers, no crew, nobody but her. The Atlantica is steaming into the mid-Atlantic and Caz is the only person on board. But that’s just the beginning of the terrifying journey she finds herself trapped on in this white-knuckled mystery.

I voluntarily read and reviewed an advanced copy of this book. All thoughts and opinions are my own.