Sherlock and Joan are set to track down a mass murderer in episode 6 of "Elementary" season 5.

Based on the synopsis for the episode, the crime-solving duo will find themselves conducting a serious investigation on a mass murder involving a chef and his customers, who were poisoned after dining at a restaurant. It turned out that the menu was contaminated with snake venom.

"Holmes and Watson investigate a mass murder when a chef and his patrons are poisoned after dining on a tasting menu tainted with snake venom. Also, Detective Bell's crush on a work colleague makes Holmes realize his and Fiona's relationship is at an important crossroads," reads the synopsis on Cartermatt.

In the promo video for the episode, a restaurant kitchen turns into a crime scene when a chef suddenly falls dead onto the ground. After the incident, Sherlock and Joan find out that the chef's patrons also died after dining at the same restaurant.

The episode will also see the return of Sherlock's love interest, Fiona.

In a recent interview with Entertainment Weekly, executive producer Rob Doherty confirmed that Betty Gilpin will reprise her role as Fiona in season 5.

"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," he said.

"Elementary" season 5, episode 6 airs on Nov. 13, 10:00 p.m. on CBS.