Meanwhile South Korean agent Jin-soo (Han Suk-kyu, ) believes Jong-sung may have information about the North Korean government's overseas slush funds.

The first half of , with its tangled web of intrigue and multilingual dialogue, has been described by some critics as dense and confusing. But as an extended chase narrative develops, Ryoo starts to incorporate the ambitiously staged action sequences he is famous for. In previous films such as (2006), Ryoo attracted notice for the gritty, realistic quality of his fight scenes. In , the action has been expanded in scope.

What's surprising is that comes so close to replicating the scale and dynamism of American blockbusters, despite an overall budget of US$9.5 million - less than half the salary of a top Hollywood star.

Ryoo says the secret to his action prowess is simply hard work. "You push your actors as hard as you can, and when they tell you they can't do any more, you break for lunch," he jokes.

South Korean directors take a different approach to shooting action sequences compared to filmmakers in Hong Kong or the mainland or Thailand, Ryoo says, pointing out that in much of Asia there is a long tradition of action films, and many stars such as Jet Li Lianjie, Donnie Yen Ji-dan and Tony Jaa are well trained in martial arts. "But in South Korea, the action genre only became established with the release of in 1999," he says. "Directors generally work with stars who only receive a small amount of training before shooting the film."

So South Korean directors have learned to make greater use of editing, props, character and other elements such as car chases to inject energy into their action scenes.

The actors in may not have much experience in martial arts, but they do have star power. "I was excited and a little intimidated to be working with four major stars, each of whom could open their own film," says Ryoo. Critics have singled out the director's brother, Ryoo Seung-beom ( ), for his chilling portrayal of an operative sent by Pyongyang to root out the informer. But the star most likely to stir excitement among overseas viewers is Gianna Jun, who first shot to prominence in in 2001. With the runaway success in South Korea of last year, and now , Jun's career is in the midst of a major revival.

Shooting of took place partly in the German city, and partly in Riga, Latvia, whose side streets can pass for Berlin and shooting costs are much lower. The international locations and multi-ethnic cast give the work a cosmopolitan feel that appealed to its investor, the Seoul-based CJ E&M. In recent years, CJ has increasingly targeted international audiences. It has co-financed films in both China ( ) and Hollywood ( ), and this summer it will release the US$40 million, English-language science-fiction film by director Bong Joon-ho ( ).

's subject matter may also boost its international appeal, given that North Korea has been so much in the news in recent months. Ryoo was first drawn to this topic after shooting a TV documentary entitled about North Korean espionage in the present day.

The director particularly wanted to capture the sense of solitude felt by many real-life spies working in a foreign land. He interviewed North Korean defectors, and was forced to update his story after the death of Kim Jong-il in December 2011.

At the same time, the filmmaker feels outsiders sometimes misjudge the situation on the peninsula. "The current political situation in North Korea is very unstable, and relations between North and South cooled under the last administration. But despite what it may seem like from the outside, we are not on the brink of war," he says.

opened in South Korea in late January, and continued to screen in February and March as Pyongyang issued threats and tensions soared between the two Koreas. But it seems most of the film's seven million-plus domestic viewers were attracted by star power and entertainment value rather than its timely political themes.

"I'm not sure if this is a good thing or a bad thing," the director says, "but young people in South Korea are far more interested in how many views [rapper] Psy's new music video has recorded on YouTube, than in whether or not North Korea fires a missile."

The Berlin File