Dr. John Watson, recently returned from war service in Afghanistan, is convalescing in London and looking for affordable lodging. He is introduced to Sherlock Holmes, a brilliant and unconventional "consulting detective," and the two agree to share rooms at 221B Baker Street.

Soon, Holmes is asked to assist in a baffling case: the body of a man named Enoch Drebber has been discovered in an abandoned house in Brixton, with no visible wounds. The word RACHE (German for “revenge”) is scrawled in blood on the wall. No valuables are taken, and the only clue is a woman’s wedding ring found on the floor.