Sherlock Holmes, Arsene Lupin, and Irene Adler meet up in London only to find a strange chess problem in the Times signed by "The Black Friar." It's written in an unknown code which Sherlock is eager to solve. The next day, the city is rocked by the news of a rich merchant found murdered. On the merchant's desk was scarlet rose: the same flower used as the calling card for a brazen criminal group that haunted the streets of London twenty years ago. Could the Scarlet Rose Gang be back?