Richard Hannay, a mining engineer on vacation from the African colonies, finds the London socialite life to be utterly monotonous. Yet when a secret spy comes into his room and hands him a coded notebook with information on the approaching outbreak of World War I, he receives more than he bargained for. Within a short period of time, both German operatives and British police are after him, mercilessly desiring the Roman numerals code, which Hannay believes he must crack himself.