Pandemonium - Book One in the 101 Ways to Hell Series

From the moment their eyes met across the crowded sales floor, Billy knew he had met his soulmate, the woman he was meant to be with. While on a date, the appearance of three hooded figures in a field spooks Aura, and she tells Billy he needs to put her from his mind, forget she ever existed. Then she was gone. But how do you forget the one you are destined to be with? The only clue to his girlfriend's disappearance is an old and very strange guide to country walks that Aura had shown great interest in-particularly Walk No.
21, which would take the traveler through "deepest, darkest Somerset." What is it about Walk No. 21 that had Aura so fascinated? And why has it become an obsession, not only of Billy's, but of anyone who has come in contact with the book?