Year 817. After an unexpected jump in time, the stellar Ark Magonia orbits the Earth of our ancestors. Damaged, it lost a graviton tank, which crashed in the Alps... A first mission is organized to recover the precious fuel. Indispensable to the intergalactic journey of the Ark, it is the only chance to reach their new planet.

Enzo and his family then discover that their return to the past is not an accident, but a willful diversion, and the plotters have just left for Earth.

Enzo and his family decide to go find the lost tank themselves.

How will our ancestors, and the prelate Agobard of Lyon, react to these beings from Magonia?