The Robinsons decide to move inland, away from the heat of the open beach. Robinson plans to build a bridge across the stream that separates the shore from the shadier woods on the other side. Robinson, Fritz, and Ernest gather lumber that washed ashore from the shipwreck while Elizabeth fashions bags and baskets to haul their supplies to their new location. The next morning, they load their supplies on the pack animals and set off, sheep and mastiffs in tow. Along the way, the boys kill a porcupine and a wildcat and discuss how best to utilize the meat and the hides.

Once they arrive at their destination—a copse of mangrove trees—the Robinsons set up camp and formulate a plan for a treehouse. Using bamboo and reeds, they fashion a rope ladder and fasten it to a high branch. Robinson climbs up and clears branches to make room for the house. Back at the beach, they salvage enough lumber from the wrecked ship to begin construction. The donkey and the cow haul the heavier pieces back to camp, and Robinson and Fritz spend the rest of the day building a floor and walls.