Sigurd Mutt returns to Barcelona. Nearly thirty years have passed. Back then he was a young cryptozoologist determined, alongside his colleagues Belaire and Sjögren to unravel the mysteries of Hidden Naturalism and trace, against the dictates of official science, the track os dangerous animals and animals that no longer exist. 'Official Science', that's what they scornfully call it, as their teacher before them did. But now, at the end of 2007, beaten and tired, Sigurd Mutt heads for Vor, a village in the Pyrenees where he intends to spend a short while in an old aristocratic spa: the Vulturó spa. He takes with him the last wishes of his colleague Belaire, which were sent to him in Hamburg together with what seems to be a fragment of an unusual text entitled Tras Columbkill. If he wants to discover its impact and meaning, he will have to complete it.