Fin O'Malley embarks on an involuntary kind of pilgrimage. He aims to climb Croagh Patrick, but the wild Irish landscape is not kind to him. He gets lost in the fog of a September day and ends up at the home of Séamus Le Brun, an old painter who lives alone in his caravan by the sea. When Séamus takes to the air, the police see no reason to intervene, but Fin's instincts are piqued, especially when two gold coins are found in the burned wreckage. The old eccentric is hiding a secret! Fin sets off on a treasure hunt. And he is not the only one. The deeper he digs, the more complicated the case becomes. And Fin must realize that leprechauns are not what they used to be.