BBC's hugely popular "Sherlock" is returning for its third season, with plenty of new developments.

The favourite detective Sherlock Holmes (Benedict Cumberbatch) will return from his fake death to take on a new nemesis, Charles Augustus Magnussen (Lars Mikkelsen). In addition to out-smarting the "worst man in London," Sherlock will have to deal with a new development in Watson's (Martin Freeman) life.

Amanda Abbington will be portraying the role of Mary Morstan. She will be the love interest of Watson. He is all set to marry her in the new season of "Sherlock." Amanda said to The Scotsman that her character will become the "third wheel" in the relationship between Sherlock and Watson.

In the original "Sherlock Holmes" series, Mary is a governess. She is introduced in the second novel of "Sherlock Holmes, "The Sign of the Four," by Sir Arthur Conan Doyle. Watson falls in love with Mary and proposes to her at the end of the book, a proposal that Mary accepts.

Amanda fears that she may face the wrath of the fans as they love Sherlock and Watson, together in "Sherlock." She told The Scotsman, "They do have this beautiful relationship, so getting in between that - which is what Mary does, she becomes this kind of third wheel -- was scary."

The actress believes that fans won't be fond of Mary. She hopes that on the "whole people really like her, because she's a great character and she has some fantastic secrets."

Amanda, 39, is a long time partner of Martin and they have two children, together.

It is highly likely that Watson and Mary will get married in the second episode of "Sherlock" Season 3. There is no official announcement yet on when the first episode of the upcoming season will premiere.

In the Season 2 Episode 3, Sherlock had jumped down from the roof of St Bartholomew's Hospital, thus faking his death. The episode also put an end to Professor Moriarty's character, Sherlock's nemesis in the first two seasons of "Sherlock."