"Castle" season 8 episode 9 is set to investigate why Rick is missing, as well as Kate's involvement in Rick's appearance.

"Castle" season 8 episode 9 is entitled "Tone Death." "Castle" showrunner Alexi Hawley told TV Line that they would be taking fans to "Castle's" missing time next. She added that that would happen not right away when the season resumed, but certainly in the middle third of the season.

Rick's disappearance took place before his wedding and was because of his old prep school friend Bilal Khan, who broke apart from Al-Qaeda to submit himself to the American intelligence. After almost dying the first time, Bilal opted to turned himself over to Rick, his trusted classmate who turned into a high profile author.

After his intercession to help his county evade an attack from the terrorists, Rick's thoughts of Bilal and the hidden op were wiped away. As a result, her was left unable to justify his absence when he was seen floating on a boat months after.

In the same TV Line interview, Hawley said that they had not nailed the story down for it; however they did like the thought that something that Castle had come across during his missing time was actually why his memory had been wiped and it had not been unavoidably due to the reason they had showed in "Castle" season 7. She added that the incident did have something to do with Beckett, but they had not nailed it down yet.

Hawley also told Christian Post that they were twisting it so that Rick and Kate were in it together, though the "public face" of them is separate.

Meanwhile, "Castle" season 8 episode 9, "Tone Dead," returns on Feb. 1.