Running on two separate tracks that intersect near the end, “The Equation” has a clever narrative structure. But its separate parts don’t quite add up.

The world-premiere play by Charles Waxberg, presented by Theatre 9/12 under Waxberg’s direction, is a morality tale in which the sins of the father (and the mother and American society) are visited upon the son.

Up on the stage, the more dominant and absorbing narrative unfolds in reverse chronological order. In the first scene, set in the Great Depression of the 1930s, a pretty, privileged young housewife, Victoria (Monica Finney), is so horrified by something she’s just learned about her physician husband, Barron (Joey Fechtel), that she promptly walks out of the marriage, and motherhood.

What has her spouse done that was so abhorrent to her? How could she ditch both a man she evidently loves and their cherished infant? One’s curiosity is piqued.

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The mystery unravels in successive scenes, clue by clue. One learns the key part a poor Russian immigrant, Pandora (compelling Colleen Carey), plays in enriching and destroying the couple’s marriage.

Without giving too much away of Waxberg’s carefully laid plot, let us just say the couple’s private sorrows and Pandora’s economic misery collide in an emotional train wreck.

Meanwhile, between their episodes, another story is going down in front of the stage via the monologue of a brash youngish man named Arash (Eric Olson). It is the 1950s, which you can tell from his boastful salesman’s spiel about selling televisions with cathode-ray tubes. Other giveaways: the cut of his suit and the martinis he swills.

It takes a while to get how Arash’s huckster rap to us (delivered by Olson in an overripe New York-ese accent) relates to what’s unraveling in reverse order on stage.

And after it does click in, so does confusion about the point of the entire exercise (which is subtitled, by the way, “a play of excavation”). The callow Arash is obviously symbolic of skyrocketing, post-World War II materialism, which is here accompanied by an unseemly callousness tinged with melancholy.

Is Waxberg’s point that the previous American generation’s sufferings are dishonored by the next, to our social peril? If so, it’s a simplistic moral take-away for a complicated setup.

As the “upstairs” drama ends, confusion sets in there too — about the real motives of Pandora, and the contrivances that bring her from the slums into a swanky Manhattan high-rise. (In a crafty touch, we see the Chrysler Building being erected in reverse, through a picture window.)

Despite the dramaturgical blurriness, and bilateral pacing of the script, the actors bring palpable sincerity to their roles. As the naive, troubled wife, Finney radiates both vulnerability and resolve. Fechtel, as the straight-arrow Barron who slips, is also affecting, as is Carey’s hard-to-read, and significantly named, Pandora.

Cynthia Geary injects some welcome humor, playing with relish a suspicious nursemaid, a madam and an assertive psychic (all of whom could be the same person, or not). And David S. Klein has an odd cameo as a dithering doc.

The hardest task belongs to Olson, whose Arash pops up to harangue and boast, as the scene changes on the stage above him. He works hard at it, but it can’t be easy playing a theatrical device whose purpose is uncertain.

Misha Berson: