Steve Grendon and Sim Jones planned, now that June days of freedom had finally arrived, to build themselves a raft and go down the Wisconsin on an exploring trip. They assumed that they would be able to talk their parents into approving the expedition, but decided they would worry about that later. Actually theirs wasn't just any old exploring trip. They had a very definite plan. They were going to hunt for treasure, the lost Winnebago treasure which Steve had read about in a history book and which might still be hidden in the cave of Bogus Bluff...