Contains spoilers for this episode and earlier episodes.
A phone call makes Moriarty abandon the swimming pool confrontation, allowing Sherlock and John to leave alive. John's blog soon brings Sherlock enough attention to attract a royal assignment. Mycroft wants compromising photographs recovered from Irene Adler, a dominatrix whose phone also holds sensitive intelligence. Sherlock approaches her home in disguise, but Irene has anticipated the visit and refuses to surrender the device that protects her.
CIA agents interrupt the confrontation over her safe. Sherlock retrieves the phone, only for Irene to drug him and take it back. She later sends him the locked handset, then apparently turns up dead. John discovers she is alive, and Sherlock learns the same after following him. The danger reaches Baker Street when the agents seize Mrs Hudson, prompting Sherlock to overpower their leader and throw him from a window.
Irene asks Sherlock to decode a message that turns out to identify an airline flight. She passes his answer to Moriarty, ruining Mycroft's plan to let terrorists destroy a plane carrying corpses rather than living passengers. Irene tries to trade her remaining secrets for protection, but Sherlock recognises her attraction to him and unlocks her phone with his own name. Mycroft later believes she has been executed and prepares a gentler explanation for Sherlock. Sherlock already knows the truth: he secretly intervened and helped Irene escape.