This book is much more than a detective story, it really is, as Adam's put it a "thumping good detective-ghost-horror-who dunnit-time travel-romantic-musical-comedy-epic". 
 This book has the witness and clever humor that is Douglas Adam's signature, which made it (at least for me) a little hard to follow (specially the ending)... I am not sure that was my fault or the story has loopholes. 
 I can't wait to put my hands on the sequel "The Long Dark Tea-Time of the Soul".