Sherlock (Jonny Lee Miller) will have a huge realization about his relationship with Fiona (Betty Gilpin) in the upcoming episode of "Elementary."

In the episode titled "Ill Tidings," the synopsis (as per Spoiler TV) reveals that Fiona is heading back to see Sherlock again. The two met in season 4 when he and Joan (Lucy Liu) were investigating a murder. Fiona is a software engineer, brilliant in her work but lacks the social skills to make friends. Surprisingly, she got along well with Sherlock. They went out on several dates. Sherlock found Fiona to be a good listener. He even confided to her the truth about his mother.

Sherlock will reportedly start thinking about what he and Fiona really have when Detective Bell (Jon Michael Hill) asks for some advice regarding his office crush. Perhaps, the episode will finally see if Sherlock will ask Fiona to be his official girlfriend.

Executive producer Rob Doherty previously revealed that Fiona would be back in the show. He said the viewers deserve to know more about her connection with Sherlock.

"We certainly owe a status report for the Sherlock/Fiona relationship. In the first few episodes there won't be much mention of her, but we are working on a return for Betty Gilpin. Fiona is a thread that we won't let dangle too long, especially considering how much we love Betty," the EP shared in an interview with Entertainment Weekly.

Meanwhile, the promo reveals that Sherlock and Joan will be tapped to investigate a mass murder. An unknown individual has allegedly used snake venom to poison not only the chef of a restaurant, but his patrons as well. In the clip, the victims are shown dying one by one. The chef had blood coming out of his eyes. Joan and Sherlock will visit one of the victims' homes where they will encounter a huge snake. With Joan close to panicking since the reptile is right behind her, Sherlock tries to lighten the situation by snapping a photo or two.

"Elementary" season 5, episode 6 airs on Sunday, Nov. 13, at 10 p.m. EST on CBS.