Her dad wanted her to run to the store, but Collette let her little brother do it. That was back in 1973, Northern Ireland. And little Dylan never made it home alive, caught in the crossfire between warring factions in that region’s long war.

Twenty years later and Collette (Andrea Riseborough) still grieves, still seems like a hollow woman. The guilt is why she’s a reliable agent for the Irish Republican Army, still part of setting up foes for murder by bomb or bullet. But her haunted face tells you her heart’s not in it.

Or, at least, that’s what the British agent who goes by “Mac” (Clive Owen) sees. He drags her in, uses her own son as leverage, and sets out to turn her into a double agent.

“Shadow Dancer” is about this “courtship.” The supposedly steely but actually fragile Collette is tempted, threatened and cajoled by Mac, who tries his darnedest to not fall for her vulnerability and those pretty, wounded eyes.

It’s an unhurried, somber thriller in the mold of Hitchcock’s “Notorious,” with the protagonists, and the viewer, unsure of which of them can be trusted, uncertain of who is falling for whom.

Gillian Anderson is ably cagey as the secretive spy boss Mac reports to, a woman with “orders” and an agenda that may clash with his own.

David Wilmot, Domhnall Gleeson and Aidan Gillen ably play a trio of IRA folk Collette has to fool as her tips are interfering with operations leading up to an attempted assassination. Director James Marsh (“The King,” and the documentaries “Man on Wire” and “Project Nim”) ably builds suspense as we see the preparations the terrorists make for dealing with a suspected traitor. They’re asking questions in one room, but in the next one, an aide is spreading plastic sheeting on the floor so that there’ll be no blood stains if an execution is called for.

Owen and Riseborough play their characters awfully close to the vest, not investing in anything that would allow this story to take the romantic or melodramatic turns we expect. But that hamstrings the movie. Screenwriter Tom Bradby, in adapting his own novel, robs the film of the higher stakes that would come into play if we felt more heat between the leads.

Thus, “Shadow Dancer” just dances around the plot points and big scenes that would have truly drawn us in.