A thriller that focuses on only two key characters shouldn’t be hard to explain, yet the plot specifics of the unexciting but sweetly old-fashioned The Numbers Station are hard to nail down. John Cusack stars as Emerson, a CIA hit man suffering a midlife crisis. To give him a rest, the bosses send him to England to guard a WWII bunker from which coded radio messages are sent to U.S. spies. Yes, shortwave radio! It’s still around! Emerson spends three days guarding Katherine (Malin Akerman), a gorgeous young cryptologist who sends number-coded assignments to secret agents the world over. All is well until the bunker’s other two agents are attacked and forced to send out 15 rogue assassination assignments. Don’t ask how, but Emerson and Katherine end up trapped in the bunker, desperately trying to find the code that will reverse those orders. Onscreen, all this makes sense (mostly), thanks to first-timer F. Scott Frazier’s well-written script. There are some decent shootouts, but the movie’s strongest assets are the soulful performances Danish director Kasper Barfoed, making his American debut, draws from Cusack and Akerman, a Swedish-born newcomer with half a dozen films in the pipeline and stardom waiting just around the corner.