Hugo Ross is perfect for the job as irascible inventor Ambrose Minstrel’s new secretary: young, completely inexperienced, and with an occasional stutter that makes him seem somewhat dim—a mug, in fact.

But from his first day, odd things begin to happen. A stranger offers him an absurd amount for an ordinary pair of field glasses; soon, the written offer is stolen from his room. A lovely girl he runs into in the dark one night outside his new employer’s house warns him not to take the job. But when she plans to meet him, and another girl arrives pretending to be her, he wonders what has become of her.

Hugo suspects something sinister and seeks out eccentric Benbow Smith, his sister’s in-law, who seems to have some relationship with the Foreign Office. Smith confirms Hugo’s suspicion that a plot to swindle the government is afoot. Turns out Hugo is not the mug the plotters think he is ... which is his greatest asset.

But before he can help unravel the plan, he must first find the girl!