This story is old news, having won the 2004 Hugo Award for best short story, but  I just discovered that you can get a free audio version (read by Neil Gaiman himself) at audible.com.

If you aren’t familiar with A Study in Emerald, it combines the Cthulu mythos of HP Lovecraft with Arthur Conan Doyle’s Sherlock Holmes to amazing effect. I have to confess that I’ve never given Lovecraft a real chance, and I’ve found the Holmes stories to be hit and miss, but this story left me wanting more of both.

Read it for free here, or listen for free here.