While exploring a cave, Bob and his sister Rebecca meet Arkana, a messenger from the city of Arkadia, deep in the centre of the Earth.

Spartakus identifies a sound, other than that emitted by the Shagma, on the other side of the crystal. Arkana asks him to cross it in order to find the city of Arkadia, but no breach seems to emerge.

In the city of Arkadia, the children note that the life without Shagshag has grown more difficult for everyone.

Spartakus, Rebecca, Bob, Bic, and Bac land in a forest where the ground is littered with very strange traces of life and the trees have been uprooted.

The hackers take a holiday under the plastic palm trees of their inflatable island, and the heroes seek to reopen an old passage.

Shagshag is exhausted and must stop in a snowy steppe. The team meet Myra and her grandfather, whose village is regularly looted by warriors.