Read most of this book from 1978 on the plane ride home where Sherlock Holmes takes on Jack the Ripper in 1888ish London. Fantastic read so far (just have the last part to go) and Sherlock is a freaking nutcase.
It gives me more appreciation for the BBC show - they definitely incorporated elements directly from this book.
Anyway it's by Michael Dibdin and it's called "The Last Sherlock Holmes Story."
Kindle version is $3 right now. Never read a Holmes story so I'm going to sacrifice half a Bacci's slice to check this out.