The spy thriller “Our Kind of Traitor” gets the first part of that equation right. [...] the movie begins well, stays there for a while and never really falls apart. Based on the novel by John le Carré, “Our Kind of Traitor” starts off with a couple on holiday, trying to blast through a rough patch in their relationship. In a restaurant one night, the man, Perry (Ewan McGregor) is approached by a boisterous Russian, who invites him to have a drink with his friends. Skarsgard locates his performance in that odd zone where appealing meets scary, and he’s by far the most interesting thing in the movie. McGregor, who goes through the proceedings looking like he’s slept in his clothes for a few days running, is nominally the protagonist, but his role is mostly reactive. [...] they’re in it — he’s the star, and she’s standing next to him — but the movie has to come up with reasons they should want to keep putting themselves in danger. The script suggests that Perry just has an exaggerated sense of duty and doesn’t care about consequences, but that’s a weak justification. In any case, it’s one thing to expect an audience to worry about characters who are dragged into trouble and struggling with all their might to disentangle themselves.