Chicago P.D. seeks help from Firehouse 51 in the upcoming episode of "Chicago Fire" season 6.

Titled "Hiding Not Seeking," next week's episode will see the city's police department seek assistance from the firehouse for a dangerous undercover mission.The major crossover continues with Voight (guest star Jason Beghe) and his team tracking down a bombing suspect. He and Antonio (guest star Jon Seda) meet with Chief Boden (Eamonn Walker), who reluctantly agrees to involve his crew and allow Dawson (Monica Raymund) and Brett (Kara Killmer) to go undercover.

While finding new leads, Boden, Casey (Jesse Spencer) and Severide (Taylor Kinney) work together with the cops and lend their skilled expertise in the case. Meanwhile, Kidd (Miranda Rae Mayo) and Zach's (guest star Daniel Di Tomasso) relationship hits a minor bump. Cruz (Joe Minoso), on the other hand, finds himself struggling with revealing his true feelings for Brett.

At the firehouse, two birthday parties are unexpectedly booked. Herrmann (David Eigenberg) and Connie (guest star DuShon Monique Brown) are tasked to come up with an alternative solution to avoid the conflict.

Reports have confirmed that season 6 will see the return of Sarah Shahi. She is slated to return to the drama as Renée for a season-ending arc. The actress, who most recently appeared on "Reverie," has been tapped to join the current installment for three episodes.

Shahi, 38, was introduced in the NBC series' first season when her character was rescued following a car accident. She had a brief romance with Severide but they immediately called it quits when she decided to move to Spain. In season 2, she came back with news that she was expecting her first child. When Severide learned that the baby is not his, they ended their relationship for good and never saw each other again.

"Chicago Fire" season 6 airs every Thursday night at 10 p.m. EST on NBC.