The much speculated third season of "Sherlock" will begin on a note of reunion that will not go as expected. Also, Sherlock Holmes will return after two years to realise that things are different now and his friend, Dr Watson is in a serious relationship and in love.

If in episode one, "The Empty Hearse," Sherlock gets to know that there is now a third wheel in his relationship with Watson, the second episode, "The Sign of Three," will throw possibily the biggest challenge of Sherlock's life. He will be called upon to deliver the best man's speech.

As reported earlier, Watson will fall in love with Mary Morstan and will walk down the aisle with her in the second episode of "Sherlock" Season 3. Since it is a wedding in "Sherlock," danger will not be keeping a distance. There is expected to be a "mortal danger" stalking the reception. Bridesmaids will assist Sherlock in solving a case and stopping a killer from commiting his crime.

In an interview, Steven Moffat and Mark Gatiss, executive producers of "Sherlock," said that the entry of Mary will put Sherlock in a domestic situation. The entry of Mary as Watson's love interest and wife puts Sherlock in a different element and there is re-assessment of things. "He (Sherlock) is suddenly not quite sure about his ground, anymore -- where he stands," said Gatiss.

"The Sign of Three" has been inspired by Sir Arthur Conan Doyle's short story: "The Sign of the Four." BBC's Official Synopsis of "The Sign of Three": "Sherlock faces his biggest challenge of all - delivering a Best Man's speech on John's wedding day! But all isn't quite as it seems. Mortal danger stalks the reception - and someone might not make it to the happy couple's first dance. Sherlock must thank the bridesmaids, solve the case and stop a killer!"

"The Sign of Three" is scheduled to air on January 05, 2014.