"Game of Thrones" season 4 star Kit Harington, who plays Jon Snow in the HBO series, will take on the role of a secret agent in "Spooks: The Greater Good," based off the hit British spy series Spooks (known as MI-5 in the U.S.). "Zero Dark Thirty" actress Jennifer Ehle will also star in the film spin-off.

Kit Harington and Jennifer Ehle star in the movie alongside Peter Firth. Firth will reprise his role from the series as Sir Harry Pearce, the head of MI-5's "Section D" counter-terrorism unit, IGN reports. "Game of Thrones" season 4 star Harington plays a character named Will Crombie, which suggests he's the son of Bill Crombie, Pearce's childhood friend and fallen MI-5 comrade.

"Spooks" ran for ten seasons in the UK. According the ScreenDaily, "Spooks: The Greater Good" is a "thriller about the dangerous fallout after a charismatic terrorist escapes from MI5 custody."

Jennifer Ehle almost played Kit Harington's mother in "Game of Thrones," according to the her "GoT" Wiki page. She was originally cast to play Catelyn Stark, Jon Snow's stepmother, but after the pilot episode was filmed in late 2009, HBO announced she was leaving the project shortly after the series was picked up. Her reason for backing out of "Game of Thrones" was that she wanted to concentrate more time on her young daughter. Michelle Fairley replaced her in the role of Catelyn Stark.

"Spooks: The Greater Good" is set for release in 2015, The Daily Mail reports.

Meanwhile, catch Kit Harington as Jon Snow in "Game of Thrones" season 4, Sundays on HBO.