Neb is rescued when a vine is lowered to him, although when Captain Harding and Herbert arrive, both deny being responsible. For Harding, it is another sign that they are not alone on the island. When the sea chest is brought back to Granite House it is found to contain a wealth of ship building tools and other supplies. Eager to get to work on a new boat, the group set out to look for materials and come across the remains of their balloon. Transporting it back down river, their raft overturns in the rapids and washes Pencroft, Gideon and Neb towards a raging waterfall. When all hands are safely rescued, the castaways return home to discover their home has been visited while they were away. Herbert and his father take their new boat out on its maiden voyage but encounter an unknown force at sea that pulls Herbert overboard…

纳布在一棵藤蔓落下时获救，但当哈丁船长和赫伯特到达时，他们都否认对此负有责任。对哈丁来说，这是另一个迹象，表明岛上并非只有他们。当海柜被带回花岗岩屋时，人们发现里面有大量的造船工具和其他用品。由于急于在一艘新船上工作，这群人开始寻找材料，并找到了气球的残骸。他们的木筏在急流中倾覆，把潘克洛夫、吉迪恩和内布冲到一个汹涌的瀑布边。当所有人都安全获救后，漂流者回到家中，发现他们的家在他们不在的时候被人拜访了。赫伯特和他的父亲乘坐他们的新船进行处女航，但在海上遇到了一股未知的力量，将赫伯特拉下船…