While the Titanic and Lusitania are both well-documented disasters, the single greatest tragedy in maritime history is the little-known January 30, 1945 sinking in the Baltic Sea by a Soviet submarine of the Wilhelm Gustloff, a German cruise liner that was supposed to ferry wartime personnel and refugees to safety from the advancing Red Army. The ship was overcrowded with more than 10,500 passengers — the intended capacity was approximately 1,800 — and more than 9,000 people, including 5,000 children, lost their lives.

Sepetys (writer of 'Between Shades of Gray') crafts four fictionalized but historically accurate voices to convey the real-life tragedy. Joana, a Lithuanian with nursing experience; Florian, a Prussian soldier fleeing the Nazis with stolen treasure; and Emilia, a Polish girl close to the end of her pregnancy, converge on their escape journeys as Russian troops advance; each will eventually meet Albert, a Nazi peon with delusions of grandeur, assigned to the Gustloff decks.