I like to think that when Batman runs into a smug 135 year old Sherlock Holmes in Detective Comics #572 and breaks off mid sentence after realising who he is, that he created a time paradox, resulting in a chain reaction that unraveled the very fabric of the space-time continuum and destroyed the entire universe.
Outside of Sir Arthur Conan Doyles original mysteries, Sherlock Holmes has been thrown all over the space time continuum in books, films, TV and yes, comics. He has been tossed in with the likes of Fu-Manchu, the Predator, Jack the Ripper and Dracula. In some instances Sherlock has even faced the creepy characters that normally reside within Lovecraft's Cthulhu Mythos. He has even been re-imagined to form entirely different characters like Gil Grissom from CSI, and Gregory House from... House. In the comics medium, whether it was intentional or not, Batman is Sherlock Holmes. You don't throw a comic book out there with 'The Worlds Greatest Detective' plastered all over it and expect for it not to garner comparisons.
So good ol' Slam Bradley is on a case in London, helping a man try to track down his kidnapped wife. Batman and (Jason Todd) Robin are also in London, scoping out the exact same scene.
Meanwhile, fanboy Ralph Dibny, otherwise known as The Elongated Man, is in London to meet a man who claims to be in possession of an unpublished Sherlock Holmes story. This unpublished story, The Adventure of the Red Leech is a key element to an evil scheme crafted by descendent of Sherlock's ultimate enemy - Professor Moriarty.
Mike Barr has created the ultimate mixture of mystery, hard-boiled private eye intensity, goofball fanboy-isms, and typical super villain bravado. It's a whole lot of awesome, smushed into 60 pages. Possibly the most impressive thing about this issue, would have to be the inclusion of ER Cruz, who illustrated the one and only issue of Sherlock Holmes for DC in the 70's. In this anniversary issue, he pencils The Adventure Of The Red Leech, giving us a sense of continuity for DC's incarnation of Sherlock Holmes.
The comic itself is a fairly easy and cheap one to come across, considering the recent surge in Sherlock Holmes' (and Batman's) popularity. You can score a copy off ebay for under ten dollars, or I am sure you will be able to find one stashed away in a box somewhere in an old bookstore in town.
Find it, read it, and enjoy it.