Triple Killer or 3XK will be coming after Rick in the upcoming seventh season of "Castle."

Executive producer Andrew W. Marlowe said that the serial killer will be one of the storylines explored in season seven. Everyone thought that 3XK was killed in season five. However, since the police couldn't find the body, Rick said that it could be part of 3XK's plan to appear to be killed by Castle, disappear and be at large conducting his killing spree.

Last season, the NYPD suffered a major blow because of infiltration and leak of information. Kate Beckett confirmed that the adversary will be back after a USB embedded in a pen was discovered from which the song "We'll Meet Again" began to play ending any doubts that Tyson is in fact back.

Moreover, the title of the first episode of the seventh season of the TV series "Castle" was finally revealed. According to reports, the title of premiere episode is "Driven" and will focus on Kate's efforts in unearthing who was behind the car crash and sudden disappearance of her fiancé Rick Castle.

Meanwhile, two new guest stars are set to join the cast of the show's next season. The two will appear in season seven's third episode entitled "Clear and Present Danger." Actor Chad Collins will play the role of Tom Talmadge, an entrepreneur of a start-up tech company who encounters mysterious circumstances. Rebecca Wisocky is also set to appear as a guest star in the said episode as Dr. Elena Sarkov, as the lead scientist at a cutting-edge research lab, whom the team consults when a pool shark is murdered by a mysterious unseen force.

"Castle" season 7 will be back on air on Sept. 29, 9PM on ABC.