New surprises will be unveiled in the next episode of "Elementary" season 4.

The upcoming episode, titled "Ain't Nothing Like The Real Thing," centers on a new double murder case that Sherlock Holmes (Jonny Lee Miller) and Joan Watson (Lucy Liu) will investigate. But as the investigation progresses, Sherlock and Joan will find out that the victims are supposedly faking a murder during the time of their real death.

But that will not be the only shocking revelation in the upcoming episode. The person whom Joan hired to spy on Sherlock and his father Morland (John Noble) will make a grave mistake. This could possibly reveal Joan's plans to learn more about the Holmes. Will this cause a problem between her and Sherlock?

Meanwhile, executive producer Rob Doherty explained to TVLine how they decided to introduce someone from Joan's family in the previous episode of "Elementary" season 4.

In the episode titled "All In," a mysterious woman named Lin asked for Sherlock and Joan's help because someone was out to kill her. Lin initially claimed that she was connected to Sherlock's brother Mycroft (Rhys Ifans), but it turned out that she is Joan's half-sister.

Doherty revealed that he became very interested in Joan's backstory, since she does not really know her biological father and her other family members.

"We also felt that we have spent a lot of time getting to know more of Sherlock's extended family this season. It struck me as a good opportunity to delve a little deeper into Joan and her family," the executive producer explained.

But while both Joan and Lin managed to patch things up during the episode titled "Art Imitates Art," Doherty stated that Lin may not appear in the next episodes of the season. However, they are still open to bringing Joan and Lin's father into the equation in the future.

"Elementary" season 4 episode 21 airs on Sunday, April 17, on CBS.