The squad will be stunned to learn Dr. Donald Mallard's (David McCallum) big secret in the upcoming episode 7 of season 13 of the long-running CBS series "NCIS."

In "16 Years," Cartermatt reports that Ducky's big revelation will come after the NCIS takes on a murder case involving a retired Navy officer. His death will reportedly force the good doctor to disclose his membership in a secret society. Apparently, Ducky has been an active participant of a group that solves cold cases. Will his connection help them solve the commander's homicide?

Last episode, a petty officer, Adam Meyers (Dante Swain) was found murdered with a sniper bullet in the chest. The local criminal with a penchant for sniper killing was apprehended earlier that day, which led the team to believe that they were dealing with a copycat. Upon investigation, it was revealed that the victim had a botched record with the Navy. He was tagged responsible for uploading nude photos of two female officers a couple of years back.

Entertainment Weekly reports that even though he confessed to the crime, Meyers got away with a light sentence. Through a colleague, Peter Woodruff (Ryan Kennedy), they learned that the victim had a confrontation with one of the women, Kara Gifford (Kelly Frye). She said, however, that she did not kill him. Kara believed he deserved what happened to him, as he was the reason the other girl, Ashley, committed suicide.

Back at NCIS headquarters, Abby (Pauley Perrette) and Ellie (Emily Wickersham) had a hard time fitting the victim's profile with that of a predatory voyeur. Upon investigation, they traced the photo to Woodruff, the whistleblower. It turned out he hated the women getting promoted ahead of him in the Navy, so he killed them. Meyers agreed to take the fall because he needed the money Woodruff would give him. His sister had been arrested for drug possession and he had to pay for the legal fees.

"NCIS" airs Tuesdays at 8 p.m. EST on CBS.