Question: Which book, which is described by the author on its cover as a "thumping good detective-ghost-horror-who dunnit-time travel-romantic-musical-comedy-epic, was turned into a comic science fiction television series called Dirk Gently?
Sentence (from "Dirk Gently's Holistic Detective Agency"): Dirk Gently's Holistic Detective Agency is a humorous detective novel by Douglas Adams, first published in 1987.
Relevant evidence: Yes