The gang befriends the Fenwicks, missionaries to Costa Rica who are spending a month at Sugar Creek enjoying fishing and their motorboat, the Vida Eterna, while giving Mr. Fenwick's ailing heart a rest.
The last swim of the summer ends miserably for the Sugar Creek Gang when someone steals Little Jim's pet baby bear. The search for the missing bear takes the gang through the woods to Old Man Paddler's cabin. When winter arrives, the boys return to the cabin, where they receive a startling surprise.