Spirou and Fantasio are spending a few days at Champignac Castle, keeping an eye on the estate while the Count is away visiting family. One night, as they are preparing to watch a comet pass in the sky, Fantasio's clumsiness causes them to lose consciousness. They awaken to the very noisy arrival of de Champignac aboard one of his strange machines except that the old man claims to be not the Count himself, but one of his descendants ... back from the future!
