It is the winter holidays at Punchbowl Farm. Dion is busy clearing the top copse and enlists everyone's help in cutting sticks, pulling stumps, and building a huge bonfire. The Jersey cow has her calf out in the valley. The rain comes to brim the lakes above the Mill House where some new friends, Ruth and Roy, have just come to live. There are interesting things to be done indoors and out, there are animals to look after, from ponies to bantams, and there is the wild wet country to enjoy. Then Lindsey finds an old map and begins to puzzle over the mysterious Frenchman's secret. Is there treasure still buried somewhere in the dam that holds back the water above the Mill House? Roy has some gunpowder; why not blow a hole in the dam and find out if there is anything there? Only a small hole of course. Much quicker than digging. The thrill of the treasure hunt that leads to this final bold move and the tremendous adventure that it causes, makes Frenchman's Secret one of the most exciting of Monica Edwards' stories.