In Book 4 of this fascinating and educational series, Peter and Grandpa are faced with the coldest winter anyone can remember. How are they going to feed the animals when the tractor has frozen solid? The first construction project is to make a snow plough for the miniature railway. However the really big project for this book is making the watermill on the river. They then have to connect it to the house to supply free electricity. Of course there are plenty of adventures (and mis-adventures!) along the way and second daring rescue at the end. Grandpa also tells some more of his amazing-but-true stories from the old railways.