The cottage in Mr Hick's garden mysteriously burns down one night, and five children think someone started the fire deliberately. Mr Goon, the local policeman, thinks so too, and isn't at all pleased to have the Five Find-Outers and Dog nosing in on his mystery.
There seem to be lots of suspects - Mr Peeks, Mr Hick's valet, has just been rudely dismissed; Mr Smellie argued with Mr Hick the day of the fire; there's a suspicious-looking tramp in the fields nearby; and even Mr Hick's housekeeper has a reason to have done it.
The children bump into Inspector Jenks fishing by the river one day, and talk to him about their theories. Inspector Jenks is senior to Mr Goon, who still doesn't want to listen to the children, and praises the Find-Outers as they reveal the true culprit - Mr Hick himself, who burnt the cottage for the insurance money.