Ep 3. His Last Vow

John and Mary's wedding day is interrupted by news of a computer hacker who has stolen classified information. Sherlock is immediately intrigued, particularly when he learns that the hacker is being controlled by a mysterious figure known only as "Magnussen". Sherlock determines to investigate and soon learns that Magnussen is a powerful businessman who has the ability to blackmail anyone he so chooses. His methods are brutal, and he seems to enjoy reveling in his power.

As the investigation progresses, Sherlock begins to realize just how dangerous Magnussen is. It becomes clear that he will stop at nothing to get what he wants, and that he has no qualms about destroying anyone who stands in his way. In a dramatic showdown, Sherlock confronts Magnussen and learns that he holds a secret that has the potential to destroy everything that Sherlock holds dear. To save himself and those around him, Sherlock must use all of his wits and cunning to outsmart this ruthless opponent.

Along the way, we learn more about the characters of John and Mary and the challenges they face as a newly married couple. We also see more of Sherlock's softer side as he struggles to navigate his complicated relationship with Mary. As always, the show is filled with tension, humor, and plenty of surprises. His Last Vow is a fitting end to an excellent season, leaving fans eagerly awaiting the next set of adventures for their favorite detective duo.