When the First World War broke out, Alfie Summerfield's father promised he wouldn't go off to fight. The next day, however, he broke that promise. Four years later, Alfie has no idea where his father is, except that he's on a special, secret mission. While shining his shoes at King's Cross Station, Alfie suddenly sees his father's name on a stack of papers belonging to a military doctor. Stunned and confused, Alfie realizes his father is in a nearby hospital, one that treats soldiers with an unusual condition. Alfie is determined to rescue his father from this strange, ominous place.