After his parents' disappearance, eleven-year-old Fennymore lives alone in an old house named Bronks with only Monbijou for company - his bike who thinks it's a horse and devours mountains of hay. Every Sunday afternoon without fail, at three minutes past three o'clock, his strange great-aunt Else turns up with an even stranger dish for lunch. When aunt Else fails to appear one Sunday afternoon, Fennymore sets off to find out what happened. In town, he discovers his aunt has died, having had too much of that quaint dish, but in a moment's inattention he loses Monbijou. Aided by Fizzy Kobaldini, Fennymore goes looking for his bike and discovers what really happened to his parents, falls foul of a silvery grey gentleman and meets an evil doctor who wants to get his hands on a mysterious invention.