"Sherlock" season 4 has begun its filming and it is rumored to present elements of extreme fear and tragedy, as reports reveal that the series is set to include a major death.

Some characters are reportedly in danger in "Sherlock" season 4. According to Bustle, they are Irene, Lestrade, Mrs. Hudson, Mycroft, Mary, and Molly. As per the publication, the series may have Irene's return and kill her, which can be a "total waste of time," since she is a "legendary" character.

Lestrade may also die in the series, since the nature of his work is perilous. Since he links Sherlock and John to the official police department, killing him removes the latter two's labels as consulting detectives.

Mrs. Hudson is a funny and kind character in "Sherlock" season 4 and her live has been put in danger for more than once. As per the publication, killing the character will leave fans in extreme sadness while Sherlock and John will be devastated.

Mycroft may be the major death in the fourth season of "Sherlock." While he and the titular character are not close enough, the latter is assumed not to cope well if he dies. Also, Sherlock would be in a "scorched earth mode."

Mary may also die in "Sherlock 4," as the character dies in the books. While she has a colorful background in the story, Mary may get involved with a tragedy, leader to her loss in the series.

Molly may also be in danger if Moriarty returns in "Sherlock 4." She is one of the major characters in the show, but helping Sherlock live once more can leave Moriarty set a nasty plot on the character.

"Sherlock" season 4 is also set to be terrible and tragic. In a statement (via Zap2It), series co-creator and executive producer Steven Moffat said that ghosts of the past were rising in the lives of Sherlock and John and terror and tragedy were looming. According to Moffat, that was the story the had been telling from the start and it was about to reach its climax.

"Sherlock" season 4 has started filming and it is set to premiere in January 2017.