Early in Mike Leigh’s thorny and satisfying “Two Thousand Years,” a youngish man named Josh lurches into his parents’ North London living room. It is also his living room, as he’s still living there seven years after graduating from university, but his furtive, almost panicked demeanor gives him the look of someone very much not at home. After catching his breath — Josh is not in the best shape — he reaches into a paper bag, sits in a hunched position, and begins a sort of rhythmic action. Has he smuggled a dirty magazine into Mum’s parlor?

While a sofa obscures much of Josh’s motions, it soon becomes clear that he is wrapping something around his bicep. Perhaps some rubber tubing in anticipation of shooting up? Then Josh stops in his tracks and frantically affixes a yamulkeh. The suspicious item affixed to his arm is a hastily wrapped tefillin — although, given his abashed ministrations, it may as well have been a Hustler or heroin. And given the response when his secular Jewish parents finally find out, those other objects may have been preferable.

Mr. Leigh’s cunningly constructed plays and films typically appear to unfold with little thought for narrative, and “Two Thousand Years” follows the same seemingly circuitous path. The confused, roiling conversion of Josh (Jordan Gelber) from bourgeois secularism to Orthodox Judaism is notably light on epiphanies or reconciliations. But don’t be fooled: Mr. Leigh and his clear-eyed director, Scott Elliott, mold the non-action into a sort of symphony of indirection, building upon each suppressed thought and swallowed insult. Taking a leap of faith is never easy but, until the play bogs down with an expendable subplot near the end, “Two Thousand Years” demonstrates with commendable patience and empathy just how trying those leaps can be for everyone involved, even those who tiptoe away from the crevasse. Josh’s parents — Danny (Richard Masur), a jovial dentist with an ethnic joke for every occasion, and Rachel (Laura Esterman), who spent the first few years of her life on a kibbutz — are perfectly willing to chew over the latest Middle East editorial in the Guardian. The subject of modern Jewry often pops up during the Saturday visits of Rachel’s father, Dave (Merwin Goldsmith), a curmudgeonly lefty who grumbles about perfidious Tories and nonexistent parking spaces. And Josh’s dogooder sister, Tammy (Natasha Lyonne), a globe-trotting translator, has brought home an Israeli boyfriend (Yuval Boim) from her latest international trek.

But these cosmetic nods to the family’s religion quickly peel away as Josh’s zeal intensifies. Rachel likens the sight of her davening son to having a Muslim in the house, and the responses range from derision to bafflement to hostility. Nearly everyone uses the vaguely dismissive Yiddishism “frummer” to describe Josh, and an exasperated Danny finally demands to know “how come a scientifically-minded university graduate, brought up in a respectable secular household, turns to God.”

Mr. Leigh is admirably loath to answer this last question. The appeal of Orthodox Judaism is nearly as inexplicable to Josh as it is to everyone else: He frequently challenges those around him to defend their beliefs, but proves evasive and vague when they turn the question on him. Tammy’s utopian ideals seem to rankle him most, perhaps because she has so little difficulty articulating them. In a society that feels increasingly unmoored — the story, which takes place between 2004 and 2005, includes brief mentions of Hurricane Katrina and the war in Iraq — the unambiguous certainty is as reassuring to Josh as it is discomfiting to everyone else.

“You can’t sort out all the answers, and then go into the world,” Rachel warns him. “You’ve got to get out there and ask the questions, and then maybe you’ll find some answers. If there are any.” Mr. Elliott is at his best when he builds the delicately fraught family dynamics, often during brief and almost silent scenes. Murmured conversations take place in the offstage hallway, spouses communicate through little more than freighted glances, and family members show years’ worth of experience in both needing and needling one another. Mr. Leigh’s famed writing method — his scripts emerge only after extended improvisations in rehearsal — pays off most fruitfully during these oblique moments. And even when Mr. Masur and Ms. Lyonne occasionally let their British accents slip, the four performers are completely convincing as a family that has allowed itself to paper over too many resentments for too long.

Alas, the mood doesn’t last. Just as the confrontations approach the outer limits of plausibility, Rachel’s self-pitying gorgon of a sister, Michelle (Cindy Katz), re-emerges after an 11-year absence. This diabolus ex machina has the benefit of allowing the family to refocus all of its animosity outward, and the lingering ill will between sisters also paves the way for a shattering monologue for the hypnotic Ms. Esterman. But the very aspect that made the previous confrontations so engrossing — the inability of the family members to speak about their feelings with any level of specificity — goes out the window as Michelle drags a bookshelf’s worth of accusations and neuroses into the conversation. Emotional punches start landing with superficially gratifying precision, but it all feels too tidy.

After Michelle storms off, however, Messrs. Leigh and Elliott somehow manage to right the ship and remold “Two Thousand Years” into its original, quietly compelling form. Nothing is forgotten, but a fair amount is forgiven. A game of chess, a lazy afternoon with a magazine, perhaps a bad joke or two — God exists in these details, too.

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