Frank (Tom Selleck) will face a complicated case involving a newly retired NYPD lieutenant in the next episode of "Blue Bloods" season 6.

The synopsis for the upcoming episode titled "Stomping Grounds" reveals that the NYPD commissioner will have to deal with the alleged crime committed by a highly respected police officer who recently retired from service.

The full synopsis reads:

"When a well-regarded, newly retired NYPD lieutenant is accused of shooting a group of potential muggers on the subway and then disappears, Frank must deal with the fallout. Also, when a drug dealer returns to Baez's old neighborhood, she and Danny must figure out how to arrest him for a murder that Baez witnessed as a child."

The trailer for the episode shows Frank thanking the retiree for all of his years in service. But when he finds out that he shot a group of subway passengers and went into hiding, the NYPD commissioner urged him to to face his crime.

However, the trailer also reveals that the alleged shooter will do everything to resist arrest. He will even put his former colleagues in danger.

Meanwhile, actress Bridget Moynahan earlier shared a few details about new cookbook titled "The Blue Bloods Cookbook." The actress, who portrays the role of Frank's daughter Erin in CBS's long-running police-procedural drama, wrote the cookbook with Wendy Howard Goldberg.

The actress revealed that some of her co-stars also contributed to complete the recipes.

"Every cast member gave a recipe. What's been nice about the cast is everyone's very different in the way they eat. Will is vegetarian. His recipe was completely different than everybody else's... it's much more of a meat-and-potatoes kind of cookbook. Tom Selleck's wife provided a recipe for Shepherd's Pie which was absolutely delicious," the actress said in an interview with CBS.

"The Blue Bloods Cookbook" can be purchased on Amazon.

The next episode of "Blue Bloods" season 6 will air on Friday, Jan. 22.