When Dr. Herman Tarnower was shot to death by longtime girlfriend Jean Harris in his Westchester County home in 1980, the newspapers fed off the story for months.

The Jewish internist and cardiologist was the best-selling author of “The Complete Scarsdale Medical Diet” and a minor celebrity. The accused wasn’t trailer trash either, but the headmistress of a hoity-toity girls’ prep school outside Washington, D.C.

The steady stream of lurid, wacky details that surfaced before and during Harris’ trial depicted their 14-year relationship as the stuff of melodrama from beginning to end. It also allowed for contrasting views of the defendant: Was Harris a jealous lover who killed Tarnower in cold blood, or a pathetically deranged figure who intended to commit suicide in his bedroom and wound up shooting him by accident during a struggle?

This tale of tragic obsession is tailor-made for the standard-issue true-crime movie that invites viewers to wallow vicariously in sordid scenes, then raps their knuckles with smarmy moralizing. But writer-director Phyllis Nagy’s slyly delicious “Mrs. Harris,” which premieres Feb. 25 on HBO, employs a post-feminist slant, an ironic soundtrack of pop love songs and some slashingly funny one-liners to achieve something far more complex and provocative.

The film begins with Jean Harris — brilliantly played by Annette Bening, who covers a stunning emotional landscape from buoyant to haggard, from loving to loony — arriving at Hy Tarnower’s house in the middle of a March thunderstorm, and depicts the events that led to his death.

As he bleeds in his bed, she recounts in bleary voiceover, “I looked at his face and he looked at me, and I guess we were both in a state of shock over how something ugly and sad could have happened between two people who didn’t argue — except over the use of the subjunctive.”

We realize that we’ve just seen Harris’ version of what happened that night, and we soon learn that she’s not the most reliable narrator. As the movie recounts their affair in flashback — intercut with scenes from the trial — Harris quarrels with Tarnower more times than you can count.

You could conclude from this and Harris’ other divergences from reality that she maintained a romantic, idealized view of the relationship that was, in fact, delusional. But she was smart, pragmatic and independent, and her emotional dependence on Tarnower perplexes even her best friend.

It’s as if Harris was shipwrecked in no-man’s land when U.S. society transmogrified in the late ’60s. She’d been sharp enough to graduate from Smith with honors, strong enough to leave a staid, unimaginative husband and raise their sons alone. But she was traditional enough to crave an old-fashioned monogamous relationship, which Herman Tarnower never signed on for.

As portrayed with reptilian charm by Ben Kingsley, the doctor is a self-made, self-satisfied success and an unrepentant womanizer. Tarnower is fond of calling himself a “country doctor with a city clientele,” but everything from his enormous Cadillac to his room full of big-game trophies puts the lie to his mock-humble act.

Kingsley, who played shrewd but powerless Jewish characters in “Schindler’s List,” “The Diary of Anne Frank” and “Oliver Twist,” revels in Tarnower’s self-assurance and selfishness. Tarnower only backs down in the presence of his mother, a German Jew of rigid bearing who has no use for the divorced, non-Jewish schoolteacher he’s dating.

By the end of the endlessly intriguing “Mrs. Harris,” which is inspired by Shana Alexander’s book “Very Much a Lady,” we’re left to interpret what really happened in this twisted romance — and the night it ended. Tarnower’s brutal honesty and pathological lack of compassion, mixed with endless prescriptions for speed and sleeping pills, certainly contributed to Harris becoming unmoored.

But Harris was undeniably a willing participant. As she remarked to her closest friend, “Cruelty isn’t a crime. Boredom is.”

“Mrs. Harris” premieres Feb. 25 on HBO.