Ryoo shot the film almost 100% on location in Europe. Filming began on April 16, 2012 on a film set in Namyang, south of Seoul, in Gyeonggi Province. After wrapping there, cast and crew relocated to Berlin, Germany and Riga, Latvia in early May 2012, and among the locations were the roof of Berlin's Westin Grand Hotel, in Schoneberg, at the Hackescher Markt, and on Pariser Platz in front of the iconic Brandenburg Gate in full view of the American and French Embassies. The shoot involved a 15-person German crew from Film Base Berlin, but the majority of production elements and talent were Korean, including around 80 crew members who brought their entire equipment. Observing that Ryoo did the recces of the locations with the actors so that they could get used to the settings, Film Base boss Mathias Schwerbock described the director as "very thorough and precise in his preparations. They are fast at shooting and very efficient."
With over 40% of the film in English, American screenwriter Ted Geoghegan was hired to construct and polish the film's English dialogue, based on writer/director Ryoo's translated Korean text.
While preparing for the film, director Ryoo Seung-wan met with several North Korean defectors and shot the documentary Spies for Korean broadcaster MBC as part of a special series that aired in 2011, intending "to make a realistic, fast-paced, Korean-style espionage action film about South Korean agents discovering North Korea's secret accounts and how political dynamics between the two Koreas get involved." Ryoo said he wanted the film to be reminiscent of Identidad desconocida (2002), and on an emotional level, to focus on the solitude and sorrow of those who live as secret agents.
A scene in which Ha Jung-woo's character gobbles a baguette was not included in the final edit, and director Ryoo Seung-wan promised fans to make the footage public when the film exceeded 3 million admissions. The clip was released on February 7.