Dick Digger, an old pal of Lucky Luke's, has struck gold in the hills. Spending the night in a hotel on his way home to stake his claim, a careless display of his new-found wealth attracts the attention of two bandits who knock him out and rob him – unwittingly taking the map to his mine with them as well! With Digger injured, it's up to Lucky Luke and Jolly Jumper to chase the thieves and recover the map.