Ambrose Minstrel, the inventor, is undoubtedly eccentric. But even his oddities cannot account for the strange events at Meade House. Young Hugo Ross, Minstrel's new secretary, feels that all the dark happenings centre somehow on himself – cryptic remarks and veiled glances between Minstrel and his assistant, stealthy footsteps in the dead of night, the offer of a small fortune for the worthless field glasses. And then there is the unknown girl who had called from the dark, the rest of her statement swallowed by the night? But in spite of all his caution, Hugo Ross is drawn into a despicable plot involving government intrigue and espionage. With his own life on the line, how much is he willing to risk for his country?

Fool Errant was originally published in 1929, and introduced the eccentric, elderly character Benbow Smith.