After dinner that first night in the grove, the father prepares for their sleeping arrangements, slinging the ship's hammocks across the high roots of the trees. Then he covers the area above them with sailcloth to protect them from possible rain and biting insects.

The father and sons then wander to the beach in search of wood to make the ladder and platforms they will build the next day for the tree house.

At first, all they find is driftwood, which is too rough. Then Ernest discovers some bamboo poles half buried in the sand, which are exactly what they needed. They cut the bamboo into five-foot lengths and bind them to carry back. The father also cuts smaller reeds to carve into arrows.

As they explore the beach, they come across a flock of flamingos. Fritz shoots one, which they will eat, and wounds another, which the father will clean for the boys to tame as a pet.

Later, when determining the height of the lowest branches, the father teaches the boys geometry and how to use triangles to measure big objects. He measures a defined distance from the trunk, then calculates angles using several measured rods, determining that the lowest branch is thirty feet off the ground.

Next, the father makes a bow and arrow. He ties the arrow with a long cord and shoots it over the limb. When the arrow drops to the ground, they have the first secured strand of what will become their ladder. Once they have knotted a rope at certain intervals and attached pieces of bamboo in each knot, they create their ladder. Tying the end to the cord lying across the high limb to the ladder, they can pull the ladder upward and secure it.

To test the ladder, the father decides that Jack, the lightest of the older boys, will be the first to ascend the tree. Fritz soon follows. Using a pulley, they haul up boards to make the first platform across the high limbs. As the father is busy constructing the platform, he hears his sons' voices above him and looks up to find them at the top of the tree, singing in thanksgiving for their new home. Although worried for their safety, he cannot bring himself to scold them.

That night, the father draws up the ladder and for the first time in many days, they fall asleep feeling very secure.