This is the answer to smelly feet - wear a clothes peg on your nose. 11-year-old Johnny Swanson is in business. He's raking in the money with his advertising scams and his agony aunt persona, Ada Ardour, who offers advice on absolutely anything in return for a shilling. But his money-making schemes are getting him in too deep. Everything is spiralling out of control, and now his own mother is in mortal danger. There's only one thing for it: Johnny must assume another role - as undercover detective.