Dirk Gently's Holistic Detective Agency

I love the bit about the horse.

Dirk Gently's Holistic Detective Agency is a ghost story, sci-fi thriller, romantic comedy, buddies-on-the-road novel which reexamines the creation of our world through literary allegory, and -- as a bonus -- takes the reader inside the thought processes of a hilariously bored horse.
Unlike the characters in Douglas Adam's epic Hitchhiker's Guide to the Galaxy series, these characters are (almost) all Earthbound, lacking extra appendages and only holding (mostly) internal dialogues with themselves. But what a fun ride it is even without the spaceships!
Richard MacDuff, a gangling computer software developer with a Chesterfield sofa trapped in his stairway, visits his former college mentor, the perennially retired Professor UrbanRichard MacDuff, a gangling computer software developer with a Chesterfield sofa trapped in his stairway, visits his former college mentor, the perennially retired Professor Urban Chronotis, called "Reg" for his title, Regius Professor of Chronology. The two attend the annual Samuel Taylor Coleridge dinner at St Cedd's College where the poet's famous works are read, igniting a series of literary allusions and historical visits redefining civilization as only Adams can concoct it.
Meanwhile, Richard's boss, software company founder Gordon Way, is having problems of his own involving an unplanned out of body experience, similar to those Coleridge is said to have had during his hallucinogen-inspired writing sessions. Rather than "a damsel with a dulcimer," Adams gives us Susan Way, detached sister of Gordon and neglected girlfriend of Richard, with a cello. There is, of course, also an ancient mariner who is tired of being "alone, alone, all all alone." (The "on a wide, wide sea" part is open to debate, though it's not as great a point of contention as the albatross.)
The title character, Dirk Gently (a.k.a. Svlad Cjelli, who also attended St Cedd's prior to the final exam-clairvoyance scandal), spots his acquaintance Richard uncharacteristically breaking and entering and appoints himself to sort out sundry strange occurrences. Prior to this, his holistic detective agency's main objective was searching for the whole cat and attempting to collect whole expenses from the cats' owners. Dirk's forceful personality cements the plot, and allows Adams to merge vastly disparate and improbable elements.
But it's the quirky characters such as Dirk's belligerent ex-secretary and the Electric Monk, whose ability to believe is a big hit in Cambridge -- with or without his horse, that bring Adam's delightful chaos to the novel.
Dirk Gently's Holistic Detective Agency is a delightful book that's even funnier the second, third or fourth read.