Season four begins with the mercurial Sherlock Holmes, back once more on British soil as Doctor Watson and his wife Mary prepare for their biggest challenge yet: becoming parents.

When Sir Charles Baskerville arrives at his family's estate from America, he finds a death threat awaiting him and a curse hanging over the family. He calls in Sherlock Holmes and Dr. Watson to solve the mystery.

When Sir Charles Baskerville is killed outside of Baskerville Hall, Dr. Mortimer fears that the curse of the Baskervilles has struck again. He enlists the help of Sherlock Holmes, before another Baskerville can succumb to the evil legend.

It is the acclaimed modern retelling of Arthur Conan Doyle's classic stories. But now, our heroes find themselves in 1890s London.

With the demise of Moriarty, Sherlock finds himself locked in another mind battle with the powerful Charles Augustus Magnussen, who is holding the secrets of the world at his fingertips. Once again, the game is on for Sherlock and John in The Empty Hearse; The Sign of Three; and finally, His Last Vow.

Sherlock Holmes has always been the smartest man in the room, until now. There is a new criminal mastermind at large, Professor James Moriarty, and not only is he Holmes's intellectual equal, but his capacity for evil, coupled with a complete lack of conscience, may give him an advantage over the renowned detective. Holmes's investigation into Moriarty's plot becomes more dangerous as it leads him and Watson out of London to France, Germany, and finally Switzerland.

Dramatization of a story by Sir Arthur Conan Doyle. The most eligible bachelor in London, Lord St. Simon, has just married a wealthy American woman. The young couple's wedding day turns to tragedy when an unwelcome guest arrives at the wedding breakfast and the bride disappears. Sherlock Holmes is plagued with terrible nightmares, which cause him to regard the plight of Lord St. Simon with contempt. Will Holmes take the case?

A beautiful young woman seeks the help of Holmes and Watson when the mysterious benefactor who has been sending her a pearl each year since her father disappeared wants to meet her. Involved are a priceless hoard of Indian treasure and a murderer, whose trademark is "the sign of four."

Sherlock Holmes, the world's most famous detective, and his trusted companion Dr. Watson pursue and solve mysteries in a variety of locations throughout England.

When assorted people start having inexplicable delusions that lead to their deaths, a teenage Sherlock Holmes investigates.

In 1947, an aging Sherlock Holmes returns from a journey to Japan, where, in search of a rare plant with powerful restorative qualities, he has witnessed the devastation of nuclear warfare. Now, in his remote seaside farmhouse, Holmes faces the end of his days, with only the company of his housekeeper and her young son, Roger. Grappling with the diminishing powers of his mind, Holmes comes to rely upon the boy as he revisits the circumstances of the unsolved case that forced him into retirement.