The Conways and the Kellys, who rule the Valley of the Smugglers, do not welcome strangers. An Excise Officer has been killed and in order to investigate the crime Detective-Inspector Napoleon Bonaparte, dressed in the disreputable clothes of a horse-thief: enters the valley one step ahead of the police, who are supposed to be chasing him. Nat Bonnay, horse-thief, in time ingratiates himself with the families, in particular with Grandma Conway, for whom he plays "Danny Boy" on a gum leaf and brings tears to the old lady's eyes. In this amusing case Bony even gives the smugglers a few tips on how they should conduct their business to avoid detection. Finally all loose ends are tidied up and the case ends with a little bit of sadness.