Attention action-film fans! There’s a fantastic new one out in theaters, just released by Lionsgate, which is a mayhem-filled fever dream from Finland, written and directed by Jalmari Helander, called Sisu. That’s a Finnish word defined at the beginning of the film, with no exact translation into English, but meaning something like “a white-knuckled form of courage and unimaginable determination” which “manifests itself when all hope is lost.”

It’s about a tough old Finnish commando named Aatami Korpi (the magnificently bearded Jorma Tommila) who fought in the 1939–1940 Winter War against the Soviets and became legendary as a one-man anti-Russian hit squad, so unkillable they referred to him as Koschel, “The Immortal.” The character is partly inspired by Simo Häyhä, aka the White Death, a Finnish military sniper reputed to have killed over five hundred enemy soldiers during that conflict. Korpi is also partly inspired by the John Rambo character in the best Rambo movie, First Blood.

Old man Korpi, we’re told, disappeared into the wild wastes of Lapland to get away from World War II, and we discover him living out there alone prospecting for gold when the retreating Nazis, in their scorched-earth spree of destruction through northern Finland near the end of the war, finally reach his desolate outpost.

Coincidentally, right before they do, Korpi finally strikes gold, such a rich vein of it that, gazing upon it, his awestruck face reflects a golden tint. Almost immediately after that, he hears the first sounds of Nazi bombings nearby that light up the horizon in sullen red. In order to cash in the gold, he has to return to the populated world, and roaming gangs of Nazis are between him and any town still standing where he could do that.

And that’s all the plot you need, really, once Korpi gets on his horse (his only companion out there other than his adorable one-eyed dog, which looks like a little lamb that rolled in soot) and rides off toward “civilization.” (It’s okay! The dog will be alright!). It seems virtually impossible that he could live long enough to redeem the gold for cash, as the Nazis are sure to kill him just for sport before they even think about commandeering the gold.

Ultimately, Korpi is caught up in the final phase of World War II in Finland, the Lapland War, when German interests in the mineral riches of the area, mainly the nickel mines, made the Nazis especially reluctant to cede the territory to the Allies. This phase of Finnish history, involving a fight for the resources of Finland, is thematized in Korpi’s maniacal determination to hang onto the gold no matter what, including an extensive scene in which he’s systematically picking up spilled pieces of gold in the road while a tank-load of heavily armed Nazis are staring him down.

Of course, it’s the Nazis who ought to be afraid of Korpi, whom they mockingly call “Grandfather,” but they don’t know who they’re dealing with. And no, action fans don’t ever get tired of the underdog, they-messed-with-the-wrong-person plot. We live for the next they-messed-with-the-wrong-person narrative, loving the moment when it all starts to turn and they realize that, for all their brutality, they’re no match for this stone-cold killer, but it’s too late to extricate themselves from the fight. A brutal Finnish World War II variation on it is just what the doctor ordered at a time when we don’t know where our next John Wick film is coming from.

Sisu is almost wordless, which is also a great gift for action fans. Haunted, weather-beaten Korpi doesn’t speak at all until the last scene, when he has two comically understated lines. Compared to him, the platoon of Nazis who take him on are downright chatty, but even they are in no mood for extended conversation.

The SS officer in command, Bruno Heldorf (Aksel Hennie), points out to his shrewd and bestial second-in-command, Wolf (Jack Doolan), that they know they’ve lost the war, and to say the least, they’re not headed home to a hero’s welcome in Germany. Jaded and bitter, they’re getting their last vengeful thrills shooting and hanging and raping and torturing Finns and burning their towns to the ground. The platoon has a group of battered Finnish women trapped in a vehicle with them, captured to serve as sex slaves. But the women, led by the severe, dark, daunting one of their number played by Mimosa Willamo, have got some sisu of their own that will turn out to be especially exhilarating once they get ahold of a few guns.

The film’s soundtrack is rich and marvelous, with deep, guttural throat singing to convey the ferocity of Korpi’s spirit as his encounters with the Nazi platoon build from shootings and knifings to tank-missile firings and minefield explosions to an underwater battle involving slitting throats to use expiring men as temporary breathing apparatuses. The crazily inventive land-water-sky escalation of fight scenes ends in a wild miner’s pickax attack to bring down an escaping Nazi plane while it’s in the air.

And the look of the film is tremendous, relying on stark, chilly Lapland plains and lowering skies to convey the grim atmosphere of the war-pounded wasteland, alongside Spaghetti Western–inspired shots of long horizon lines cut by stark, upright figures facing off, or bold close-ups of hard fierce faces, slack sneering ones, or in one memorable case, a startled round-eyed face with a big knife plunged through the temple. The gore flies thick and fast, and bright gold and red lettering for the chapter titles present cheerfully incongruous warnings of mayhem to come such as “The Nazis,” “Minefield,” and “Legend.”

The film is doing very well in limited release, especially for a Finnish action-film curiosity. But you should hurry out to see it, because it’s not getting nearly enough admiring press to help push it along, and it’ll need word-of-mouth promotion.

I guess the question is, are you in the mood to see Nazis get what they deserve in exhilarating bursts of rough justice? Given the state of the world now, I can’t imagine why you wouldn’t be.