“When you strike at a king, you must kill him.” – Ralph Waldo Emerson

Sean Ellis’s new film “Anthropoid” starts in the snow and ends in the rain, with little sunshine in between. Sadly, the heroic mission, one among many botched World War II adventures, only winds up validating Emerson’s words.

The story: In 1938, Britain’s appeasement of Hitler led to the betrayal of Czechoslovakia, throwing the Czechs under the Nazi boot and specifically, under the domination of one of the most evil of all Nazis, Reich-Protector Reinhard Heydrich, third in command under Hitler himself, and the principal architect of the “final solution,” earning him the nickname “Butcher of Prague.”

Thus, under pressure from escaped Czech fighters, British Intelligence decided to parachute a group of former resistance fighters now stationed in Britain, with orders to assassinate Heydrich, even though, surely, some among them must have considered the horrible and inevitable unintended consequences. If you’re younger than 70, none of this will ring a bell for you. That’s good. Don’t read anything more, just enjoy it as a splendidly made action adventure. “Anthropoid” delivers those unintended consequences in full color, ear splitting sound and shattering depictions of the sadistic Nazi revenge upon the citizenry of Prague.

Prepare yourself. There will be blood here. There will be heroism, a few packets of romance, and a 20-minute finale that will rattle your popcorn.

The film, expertly and realistically done, focuses on the two who were sent to enact the job: Jan (Jamie Dornan) and Josef (Cillian Murphy), along with a band of fellow patriots.

Ellis’ film is stark, bloody and unrelenting; he pulls no punches. The enemy here, along with the traitors who assist them, are, with few exceptions, presented unsentimentally and with cold precision. There are no funny Mel Brooksian Nazis, softhearted, generous or gracious masters among them, such as we saw in Roman Polanski’s “The Pianist.”

Regrettably, some Hollywood sentiment folds in to soften the many blows. Both commandos are Hollywood handsome heroes, who stand out in comparison to their fellow agents, who all look ruggedly real and speak with the proper accents. Research, however, reveals that the actual commandos were indeed handsome fellows.

This makes it necessary to bring in two lady resistance fighters for some much needed love interest: Marie (Charlotte Le Bon) and Lenka (Anna Geislerova), both of whom really could speak Czech. Both are impressive.

Tiny, bespectacled Toby Jones (“The Hunger Games”) is aboard as “Uncle Hajsky,” a tweedy, rumply librarian who headed up what was left of the resistance. Toby is a first-rate pro but still looks eerily like Truman Capote, a role he dazzled us with in Douglas McGrath’s 2006 “Infamous.”

What really stands out is Ellis’ cinematography, clearly done with Radek Hanak’s art direction. Together, they give us a grim 1942 Prague with the snowy streets, foggy bridges and cramped hideouts in the bowels of a cathedral. I remembered that, as a boy, I had seen the same story done in Fritz Lang’s 1943 “Hangmen Also Die,” with a script by Lang and Bertolt Brecht, both artists who had fled Nazi Germany.

We’re left with the truthful but sad realization that the end in no way justified the means.

Heydrich, wounded in the attack and only dying weeks later, was about to leave for Paris that morning, and then return to Berlin. It seems the whole plot hatched by backroom heroes in London was a dire miscalculation, rife with mistakes that resulted in a monstrous retaliation and massive loss of Czech life.

Dornan, not a bad actor, is as handsome and unblemished a parachuting warrior as you can get. Irish actor Murphy is always too pretty to die, but hits his marks and delivers his lines well. He will, however, have to study up on his method acting, as he is set to work alongside three of Britain’s greatest actors: Tom Hardy, Mark Rylance and Kenneth Branagh, in Christoper Nolan’s World War II drama “Dunkirk,” another history epic that will confuse those younger than 70. “Anthropoid” a history lesson you will not forget.

J.P. Devine is a former stage and screen actor.