Six hundred and fifty-seven days ago, Meg Kenyon's father left their home in France to fight for the Allies in World War II, and that was the last time Meg saw him. Recently, she heard he was being held prisoner by the Nazis, a terrible sentence from which Meg fears he'll never return. All she has left of him are the codes he placed in a jar for her to decipher, an affectionate game the two of them shared. But the codes are running low, and soon there'll be nothing left of Papa for Meg to hold on to at all.