It’s almost gotten to the point that if you want a good, rousing World War II thriller about good guys fighting dastardly Nazis, you have to look to Europe rather than Hollywood; for the most part it’s there that the old-fashioned virtues of mood and structure survive. “Valkyrie” may have been a recent exception, but even Bryan Singer’s superhero movies have exhibited an old-style craft that eludes most young American directors. And if you were looking for a worthwhile example of a modern “Casablanca,” the choice wouldn’t be a stumbling snoozefest like “Shining Through” but Paul Verhoeven’s quick-paced, invigorating “Black Book.”

Now there’s another possibility—Danish writer-director Ole Christian Madsen’s “Flame & Citron.” It’s the fact-based tale of two young men, Bent (Thure Lindhardt) and Jorgen (Mads Mikkelsen), who become folk heroes as resistance assassins who target influential collaborators during the German occupation of their country. Operating in Copenhagen, they systematically eliminate targets like politicians ands newspaper editors they’re assigned to kill by group leader Aksel Winther (Peter Mygind), a lawyer who takes instruction from British command. As their notoriety grows, they’re given the nicknames Flame (from Bent’s red hair) and Citron, and earn first place on the “wanted” list of local Gestapo chief Hoffman (Christian Berkel).

This being a contemporary film, of course, their story is not told in black-and-white, either literally or figuratively. Visually it’s shot in widescreen by Jorgen Johansson in a suitably muted color palette that captures the somber atmosphere of a city under siege, with occasional flashbacks drained of color entirely. The cinematography perfectly matches the period detail fastidiously fashioned by the behind-the-scenes crew, as does the sorrowful score by Karsten Fundal.

And in narrative terms the script, set in the middle of 1944, when the tide of war was definitely turning, is also a matter of shadowy grays. Bent and Jorgen aren’t portrayed as simple heroic types; they’re a flawed and conflicted pair. Bent’s father is a resort-owner who hosts Hoffman, and while he seems self-controlled, he’s a thoughtful fellow who harbors doubts that sometimes interfere with his ability to carry through on assignments—like an order to shoot a smooth-tongued quisling named Gilbert (Hanns Zischler). His involvement with a mysterious courier named Ketty (Stine Stengade) also proves dangerous. By contrast Jorgen is an emotional wreck whose wife, tired of his long absences, has found romance with another man and moved in with him, along with their young daughter; and while adept as a driver and general fixer, he’s never actually killed anybody and may be incapable of doing so.

The men, moreover, are working in an environment murky with suspicion and double-crosses. Is Ketty a double agent, and can anything she says be trusted? Is Gilbert really pro-Nazi, or a Danish sympathizer? Is Winther what he seems, or something more sinister, and are there traitors in his group? And what of the leadership of the Scandinavian resistance represented by Spex (Flemming Enevold), whose injunctions against violence clash with Flame and Citron’s ever more reckless, vengeful conduct—and lead to an act that the men themselves regret, and that brings down brutal retaliation from Hoffman?

It isn’t always easy to keep an accurate scorecard as you watch “Flame & Citron”—Danes more familiar with their own history will have an easier time than audiences elsewhere, since Madsen and his co-writer Lars K. Andersen have crammed so many incidents and subtle suggestions of nefarious goings-on and psychological byways into their narrative that the film goes on to epic length and sometimes gets confusing or feels a bit repetitive.

But in a way the fact that the story is little known—and the actors, while all solid, equally unfamiliar—is beneficial. Since most of us don’t know how the men’s tale will end, it keeps one wondering until the very end, and the ending is sad but satisfying. The result is a suspenseful, often riveting drama of World War II resistance that combines old-fashioned virtues of craft and style with a more modern sense of nuance and complexity.