Season 4 of "Elementary" returns with an all-new episode "Ain't Nothing Like the Real Thing" airing this Sunday night.

In the upcoming episode, Sherlock Holmes and Joan Watson take on a new double-homicide case. However, as they begin to investigate the case, they realize that the victims were just initially staging a fake murder before they were killed.

According to the promo, "Ain't Nothing Like the Real Thing" will once again see the return of Sherlock's unusual investigative methods, which begin to annoy his colleagues. Although these tactics may be unusual, they lead to very informative discoveries.

Meanwhile, Watson's source inside Morland Holme's office runs into some trouble that may threaten to expose her spying on both Sherlock and his father. Will Watson's sleuthing ways prove detrimental to her relationship with Sherlock?

During the earlier part of the season, Sherlock and Watson were tasked to determine who would possibly want Morland dead. While the past few episodes made no mention of this pending case, viewers can expect the last few episodes of the season to finally resolve this storyline. The next few episodes will see Morland encounter more trouble, probably at the hands of his nemesis.

Despite fans' requests, season 4 has not featured the return of Jamie Moriarty — Holmes' former lover-turned nemesis — largely due to actress Natalie Dormer's busy schedule. However, it has been revealed that upcoming episodes will also feature a Moriarty-centric storyline.

According to TVLine, Tony Curran has been tapped for a guest appearance as Joshua Vikner. His character is described to be an economics professor who has taken an academic interest in Moriarty. He will be crossing paths with Sherlock and his father in the final episodes of the season, and the information he possesses will have a big impact on the show going forward.

From everything that has been revealed, it seems that the last few episodes of "Elementary" are bound to be very, very exciting.

To see how everything unfolds, be sure to catch "Ain't Nothing Like the Real Thing" airing on Apr. 17, Sunday, at 10 p.m. ET on CBS.