• Nathan Fillion is known for playing Richard Castle in the ABC series "Castle."

Nathan Fillion is known for playing Richard Castle in the ABC series "Castle." (Photo : Facebook/Nathan Fillion)

"Castle" Season 8 ended mid-season in 2015 in episode 8 titled "Mr. & Mrs. Castle," in which Richard Castle (Nathan Fillion) and Kate Beckett (Stana Katic) were trapped at sea with the killer of a cruise ship entertainer while investigating the murder. The ABC drama series created by Andrew W. Marlowe is set to return on ABC on Feb. 8, Monday.

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In "Castle" Season 8 episode 9 titled "Tone Death," Castle and Beckett have to be careful when it comes to keeping their secret. In an exclusive sneak peek obtained by Entertainment Weekly, the two characters by Fillion and Katic are seen sneaking off to have a secret date when nobody is looking.

In order to continue working with the 12th precinct while keeping his secret with Beckett, Castle has to come up with a convincing cover. However, his plan will lead to some problems because others will be negatively affected.

What fans can expect from "Tone Death" is that the spark between Castle and Beckett is back. Having secretly reunited, the two deftly give each other an apology amid their faked breakup and fights, according to TV Line.

Directed by Hanelle M. Culpepper, "Tone Death" also features the characters Martha Rodgers (Susan Sullivan), Javier Esposito (Jon Huertas), Kevin Ryan (Seamus Dever), Lanie Parish (Tamala Jones), Alexis Castle (Molly C. Quinn) and Hayley Vargas (Toks Olagundoye).

Aside from playing the title role in "Castle," Fillion is also set to star in "Yamasong: March of the Hollows" opposite Freida Pinto and Abigail Breslin and "Henchmen," in which he will voice Captain Superior. Meanwhile, watch a clip of his recent appearance on "The Late Late Show with James Corden" here: