Some words I jotted down and scratched out as I took notes on “Plan A,” an historical thriller about Haganah, Nakam and the post-war plot to exact revenge upon Germany for killing six million Jews during the Holocaust.

“Melodramatic.” OK, that works. “Ahistorical.” I shouldn’t say that because the picture teases us in trying to have it both ways, historical and a history-twisting fantasy. We get a taste of the real history, if not its literal truth. “Unaffecting.” It’s rare that a Holocaust drama doesn’t move you, and this one struggles to find its emotional core.

This really happened. Nakam, the Hebrew word for “revenge,” was a real group of Holocaust survivors hellbent on making the German populace pay, en masse, for condoning and/or participating in genocide. Their “Plan A” was a mass poisoning of a city’s water supply. It’s a fascinating piece of little-known history and well worth a filmed treatment.

But it proves a slippery subject for Israeli co-writers/directors Yoav Paz and Doron Paz. Their fictionalized take on it gives us an invented eyewitness/infiltrator of Nakam, a necessary plot device to give the viewer someone to identify with. And they try to credit the future State of Israel and its Haganah paramilitary group for leading the hunt for this rogue band of avengers, trying to prevent an event that could only have been remembered in infamy. That doesn’t seem to jibe with the historical record.

August Diehl of “The Last Vermeer” and Netflix’s “Munich: The Edge of War,” is Max, a haggard, filthy camp survivor when we meet him. He’s returned to his family’s rural German home after being released from a concentration camp, and his greeting is a beating from the Nazi sympathizer who ratted him and his missing wife and daughter out to the Gestapo.

“Just because the war is over doesn’t mean we can’t kill Jews anymore,” the home’s treacherous new owner hisses between blows.

Max is traumatized, weak and wandering. He meets an aged survivor (Yehuda Almagor) who passes on rumors about where they can go for food, transport and information about lost loved ones, and he cackles and rants that “The dead give you no rest.” He’s trapped death in a cloth bag he keeps on him, he insists.

The metaphor? Grief and lusting for revenge will eat you alive.

But when Max falls in with members of Britain’s Jewish Infantry Brigade who have undertaken their own off-the-books post-war mission, he may have found his purpose. He observes as their leader, Michael (Michael Aloni) “enhanced interrogates” a town burgher, demanding names of Nazis who have slipped back into the local population.

Max is shocked when this leads to summary executions by the score. Should he join in, or should he settle in a refugee camp with the hopes of emigrating to Palestine? Then word of another, even more extreme group, catches his ear. When asked, he volunteers to infiltrate Nakam, get close to its charismatic leader, Abba Kovner (Ishai Golan) and find out what they’re planning.

Because whatever the Jewish Brigade and its undercover Haganah members are up to on the sly, Nakam is planning something big. “I want my revenge. I deserve it,” has gotten him into this world. And these people, among the first to use the phrase “Never again” intend to do something about it.

The film is about the battle of conscience within Max, who cannot “move on” himself, and yet is troubled by the fanatics he has joined.

“These people are not victims,” the haunted widow Anna (Sylvia Hoeks of “The Girl in the Spider’s Web”) declares. “They heard our screams! An eye for an eye, six million for six million!”

The dialogue is sharp, quotable and accusatory.

And it’s not hard to identify with characters who know “the courts and their so-called justice” will “never get them all.” There were serious proposals that Germany be de-industrialized, its populace scattered and its economy reduced to farms at the end of the barbaric war a nation of Hitler cultists unleashed. However the world would have reacted to a mass murder of Germans in ’45-46, the passage of time hasn’t watered down the feeling that they had it coming.

But the characters and performances rob this story of much of its pathos and empathy. The pacing’s a bit slack. One of the cinema’s most clumsily shoehorned-in love/sex scenes doesn’t help. And the “have our revenge and rise above it” tease messaging of the third act is a blunder.

“Plan A” starts with promise, and features that rare novel take on The Holocaust as a subject. But the fascinating history isn’t truly given its due, the suspense never has a chance to build and the characters and the cast playing them don’t make that leap from “competent” to compelling.”

Rating: unrated, graphic violence, torture, sex

Cast: August Diehl, Sylvia Hoeks, Ishai Golan, Yehuda Almagor and Michael Aloni

Credits: Scripted and directed by Yoav Paz, Doron Paz. A Menemsha release.

Running time: 1:49