‘Red Joan’ provocative true story

Judi Dench is the one marquee name associated with the movie “Red Joan.” But really, with her on board, who needs more than one?

Yet as good as she is, the actress is little more than the framing device for this polished and morally provocative — yet hardly pulse-pounding — tale, loosely based on the life of English spy Melita Norwood. (In her 80s, Norwood, hardly a household name, was exposed for handing atomic secrets to the Russians, dating back to World War II.)

Opening with the 2000 arrest of Dench’s fictionalized Joan Stanley, and structured as a series of police interrogations, the story is largely told in flashbacks, beginning in 1938, as a young Joan (Sophie Cookson) is gradually radicalized by her Communist lover, Leo (Tom Hughes), and recruited by the KGB.

“My little comrade,” Leo calls her, over and over.

Cookson and Hughes both deliver fine performances, under the irreproachable staging of theater director Trevor Nunn, working from Lindsay Shapero’s adaptation of Jennie Rooney’s 2013 novel. But the action (if that’s the right word) moves pretty darn slowly, with Joan, who takes a job working with British nuclear scientists on the code-named “tube alloys” project, hesitating to even dip her toe into espionage until after the United States has already developed — and dropped — its bomb on Japan.

The film argues, persuasively, if somewhat one-sidedly, that Joan wanted to even the playing field, assisting Russia in the development of its own nuclear weapons as a way to deter any single nation from using them.

Such ethical nuance will not necessarily convince everyone. Joan’s grown son (Ben Miles), a lawyer, represents the skeptical side of things, denouncing his mother as a traitor, after he gets over his shock and disbelief. But even he eventually comes around.

“Red Joan” is ostensibly a spy drama — “thriller” may be overstating it — but at heart it’s more like an antiwar film. Much of the story concerns Joan’s romantic relationships: first with Leo, and then later with her boss (Stephen Campbell Moore). But Joan’s true passion — and the film’s, which it proudly wears on its sleeve — is for peace, even at the cost of patriotism.

Or at least as that word is traditionally defined. “I love my country,” the elder Joan says, with a fervor approaching defensiveness. As delivered by Dench, those words don’t land like the rationalization of a turncoat.