In the fall of 1918, a fever gripped Boston. The streets emptied as paranoia about the deadly Spanish flu spread. Newspapermen and vigilante investigators aggressively sought to discredit anyone who looked or sounded German. And as the war raged on, the enemy seemed to be lurking everywhere: prowling in submarines off the coast of Cape Cod, arriving on passenger ships in the harbor, or disguised as the radical lecturing workers about the injustice of a sixty-hour workweek.