Four months later, the Gratan has finally been repaired and the companions will soon set off for Africa. But first the balloon must be repaired. While Ayerton tries to seduce Grandis, Jean and Nadia make a remarkable discovery about their island home: there is an underground factory which resembles their former subaquatic home. While exploring, Nadia falls into a trance and mysteriously disappears behind a wall, leaving her clothes in Jean's hands.