Most people know Douglas Adams as the author of the Hitchiker's Guide To The Galaxy series of books.
However, he also wrote two books featuring a detective named Dirk Gently who runs the agency mentioned in this post's title.
BBC Radio 4 has just started running a serialisation of the first book.
Fortunately for those of us outside the UK, each episode can be heard as an audio stream for six days after it airs, by going to the show's website.
Alternatively, here's a direct link to the audio stream.
The next episode airs on October 10th, so be quick!