For months, Professor Bell has been plagued by dark nightmares. The threats from his adversary Adam Worth, who has sworn revenge for the death of his daughter, are slowly driving him insane. When he nearly strikes one of his students in a fit of madness, Bell is suspended from the university. To regain his composure, he embarks on a cycling tour of Northern Ireland with his assistant Ossour and the Victorian ghost Eliphas. However, instead of rest and peaceful sleep, the companions encounter zombies, goblins, and a castle in the sky, where Professor Bell is abruptly taken after some turbulence. In this tricky situation, only the unusual methods of the elfologist Petrus Grumbart can help. In the fifth volume of the Professor Bell series, Joann Sfar and Hervé Tanquerelle once again succeed in telling this peculiar and fascinating story.