Jim Moriarty (Andrew Scott) may be dead, but his evil plans could continue following Sherlock Holmes (Benedict Cumberbatch) when "Sherlock" returns for season 4.

During the last Christmas special, titled "Sherlock Holmes: The Abominable Bride," the supposedly dead villain appeared in Sherlock's dream as the bitter rivals faced each other at the Reichenbach Falls and Baker Street. But since it was confirmed that the character is really dead, several speculations say that Moriarty could have a twin brother who will avenge his fate against the sly detective.

According to a theory from What Culture, Sherlock might have spilled the beans regarding a Moriarty twin plot during the Christmas special when he said "It's never twins, Watson!"

The statement could be the subtle hint that was incorporated by series creators Steven Moffat and Mark Gatiss to tease fans about the plot for season 4.

Moffatt also confirmed in a statement,as reported by E! News, that Sherlock and his loyal friend Dr. John Watson (Martin Freeman) will be haunted by their past.

"Ghosts of the past are rising in the lives of Sherlock Holmes and John Watson and terror and tragedy are looming. This is the story we've been telling from the beginning and it's about to reach its climax," the series co-creator said.

Aside from the threat of Moriarty's return, a new villain is confirmed to join the series in season 4. According to reports, "Harry Potter" star Toby Jones will play the role of Sherlock's newest nemesis next season.

BBC revealed that Jones is set to appear in the second episode of the three-part series, which will be directed by Emmy Award-winning director Nick Hurran. Both Moffat and Gatiss announced their excitement over Jones's participation in the series.

"We're thrilled to welcome one of our finest actors to the Sherlock family. I know Toby will embrace the part with true relish!" Gatiss stated, while Moffat added that he is "Delighted to have Toby Jones on board, bringing to life one of Doyle's finest villains."

"Sherlock" season 4 is expected to return to BBC in January 2017.