Sherlock's on the case as his world begins to crossover with the Moriarity Brothers and their underworld machinizations. Both groups find themselves entangled with Irene Adler, a courtesan with high-ranking clientele. Her latest actions threaten the British Crown as we see Sherlock's brother Mycroft hiring Albert Moriarity with retrieving classified information and silencing Adler permanently. Meanwhile, Irene hatches a plan to endear herself to Sherlock in the hopes of preventing her assassination.