A patterned string of deaths has been appearing in Europe, all the victims turning up unscathed. The suspicious presumed-to-be-homicides catch the attention of Bobby, who then sends Sam and Dean to London - the predicted location of the next target - to set things straight. When the brothers get there and begin investigating, they come across Sherlock Holmes and John Watson, who are also working on the case. The four end up collaborating on the investigation, only to have things go horribly wrong when time runs short.