It tells the story of four individuals in World War II who make their way to the ill-fated MV Wilhelm Gustloff.

The story also touches on the disappearance of the Amber Room, a world-famous, ornately decorated chamber stolen by the Nazis that has never been recovered.

She writes in her Author's Note for the novel that even though the sinking of the Wilhelm Gustloff is the deadliest maritime disaster in history, "remarkably, most people have never heard of it."

Stories of war are often read and discussed worldwide by readers whose nations stood on opposite sides during the battle.

Sepetys father's cousin wanted the story to be told as a way to give a voice to those who lost their lives on the Ship.

[4] Sepetys goes on to say, "And I was fascinated by the story, wondering why it is that some parts of history penetrate our collective consciousness, and others remain hidden?"

So I wanted to write from that point of view, which is why I have four alternating main characters, all young people from different nations, seeing life from four different cultural lenses on this refugee trek."

The book follows four central characters as they evacuate their home countries: Emilia, a teenage Polish orphan;  Florian, a restoration artist from East Prussia; Joana, a Lithuanian nurse; and Alfred, a Nazi.

It is revealed that fifteen-year-old Emilia is eight months pregnant after an assault by Russian soldiers; Florian, the restoration artist, is on the run for stealing a piece of art from the Amber Room; and Joana is secretly a "murderer".

While on the boat, Emilia gives birth to a daughter, Halinka; Joana works as a nurse; Florian hides from Nazis who are looking for him since he stole an artifact from the Amber Room.

In reviewing the book, Anderson wrote, "once again, Ruta Sepetys acts as champion of the interstitial people so often ignored — whole populations lost in the cracks of history.