Premise: Salt to the Sea is a 2016 historical fiction young adult novel by Ruta Sepetys. 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 work of art stolen by the Nazis that has never been recovered.
Hypothesis: Salt to the Sea involves the setting of Word War I.