The woman:A Scandal in Belgravia.

After finishing their confrontation with Jim Moriarty in "The Great Game," Sherlock Holmes (Benedict Cumberbatch) and John Watson (Martin Freeman) are back on the scene (Andrew Scott). After a phone call breaks the potentially life-threatening exchange between Moriarty and Sherlock, Moriarty withdraws and orders the snipers to leave the scene.

Holmes has gained some notoriety as a result of Watson's blog posts on the cases they've solved. One day, Holmes and Watson are summoned to Buckingham Palace, where they are introduced to Mycroft (Mark Gatiss). Mycroft discloses that Irene Adler (Lara Pulver) took incriminating images of herself with a female member of the royal family, which she then sold to a magazine for profit. The authorities are attempting to recover Adler's smartphone, which has the images in question. Holmes and Watson attempt to gain entry into Adler's home through trickery, but she is prepared for them. Holmes encounters Adler completely undressed, rendering him unable to deduce anything about her.

In the midst of purposefully setting off the fire alarm, Holmes discovers Adler's concealed safe, which he had previously just glanced at uneasily. All of a sudden, many Central Intelligence Agency (CIA) agents, lead by Neilson (Todd Boyce), break into the residence and demand that Holmes open the safe. When Holmes cracks the password, the ensuing mayhem results in the deaths of several agents. Adler then sedates Holmes, steals the phone, and flees with it. Holmes and Adler are both arrested.

It is Christmas Eve when Holmes discovers that Adler has sent him her phone number. Given the significance of the phone, Holmes believes she is likely to die in the near future. Indeed, the authorities discover a disfigured body that has been identified as that of Adler.

After that, on New Year's Eve, Watson runs across Adler, who is still alive despite having pretended to be dead. Holmes tracked them down and discovered the truth as well. Meanwhile, Mrs. Hudson (Una Stubbs) is being held captive by Neilson's crew, and Holmes manages to restrain Neilson. Adler arrives and informs her that she is still being sought after. She wants Holmes to decrypt a code that she has stolen from the Ministry of Defense. Sherlock deciphers it with ease, showing that it is a list of airline seat allocation numbers, as predicted. Adler informs Moriarty of this information, and Moriarty taunts Mycroft Holmes by claiming that he (Moriarty) now understands their strategy.

A government employee transports Holmes to Heathrow International Airport. It has been confirmed by Mycroft that the government planned to fly a jet full of corpses in order to avoid alerting the terrorists who were intending to bomb the plane, eerily similar to the Coventry legend. However, because Holmes unknowingly assisted Adler (and, as a result, Moriarty) in cracking the code, the plan was thwarted. In exchange for the contents of her phone, Adler divulges a list of demands to Mycroft, which includes protection among other things. Sherlock, on the other hand, deduces Adler's feelings for him and concludes that the password is "SHER." As a result, the words on the screen read "I AM SHER-LOCKED" when they are all put together. After losing her advantage, Adler begs Sherlock and Mycroft for protection, but they refuse to grant her request.

Mycroft informs Watson that Adler has been slain by terrorists, but he intends to inform Holmes instead that she has been placed in a witness protection programme in the United States. Holmes requests Adler's phone and informs Holmes that Adler's final text message was "Goodbye, Mr. Holmes," implying that she has passed away. Following Watson's departure, a flashback reveals that Holmes had disguised himself as the executioner and had rescued Adler from certain death.