The sophomore feature by the writing-directing team of sisters Jill and Karen Sprecher (“Clockwatchers”) is a mini-“Magnolia” or pint-sized “Happiness” of interlocking stories that are essentially variations on a theme. It has neither the visual flair of Paul Thomas Anderson’s epic- length opus nor the dark humor of Solondz’s suburban reverie (or of his more recent “Storytelling”), and its concerns aren’t quite so existentially profound or so smoothly presented, but in its modest way it’s nearly as fascinating.

The plot threads of “Thirteen Conversations About One Thing” fall essentially into four parts. One involves a hot-shot prosecuting attorney, Troy (Matthew McConaughey), whose confidence and self-righteousness are challenged when he’s involved in a terrible accident. Another centers on Walker (John Turturro), a rigid, self-controlled physics professor who cheats on his wife Patricia (Amy Irving) while treating one of his more lackadaisical students (Rob McElhenney) with disdain. The third focuses on Beatrice (Clea DuVall), a cheerful young cleaning woman whose outlook is threatened by difficult circumstances. And the last deals with a cynical insurance supervisor (Alan Arkin) who finds one of his agents, the irrepressible Wade (William Wise), intolerably jovial and sets out to prove that his sunny disposition is unwarranted.

It wouldn’t be fair to reveal precisely how the Sprechers tie these various story strands together; suffice it to say the links don’t strain credulity overmuch (as, for instance, was the case in last year’s overpraised ensemble piece “Lantana”) and that the outcome–or outcomes, to be more precise–have a satisfying sense of inevitability without being pat. There’s an overarching concept at work throughout–the search for happiness, or, to put it another way, the struggle between optimism and pessimism–but it’s handled gently, almost shyly, and so doesn’t seem oppressively obvious. (The message is the same as the one that, in the old story of Herodotus, Solon gave to King Croesus–you can never say that a man is truly happy until you know the condition in which he dies.) The conclusion that the film draws from its ruminations on this theme–that people should try to show a little kindness to others–is hardly earth-shattering (and may strike you as a bit sappy), but the sincerity with which it’s presented feels authentic. “Conversations” also has a touch of the sort of playfulness in dealing with time that Tarantino showed in “Pulp Fiction” and Nolan in “Memento,” and that makes the narrative more intriguing. “Life only makes sense when you look at it backwards,” a character remarks at one point, and the same might be said of the picture as well.

Much of the success of the film in dealing with these matters lies in the astute casting. Arkin anchors the tale with a wise, beautifully textured performance, and McConaughey is very nearly as fine; this turn, along with his expert work in Bill Paxton’s “Frailty,” shows that he’s recovered the early promise he largely lost in a succession of big Hollywood flicks. Turturro’s quiet, introverted performance recalls “Barton Fink,” and DuVall proves suitably eager and likable. Irving hasn’t as much screen time as the others, but she uses it well–she’s touching and restrained as the wronged wife.

“Thirteen Conversations About One Thing” won’t win any technical awards: it’s a simple, spartan piece, unostentatiously filmed on location without any frills or finery. Jill Sprecher’s direction, too, is very straightforward and unaffected–unassertive is perhaps the most descriptive term. The plainness of the result is entirely appropriate to the script, which would have suffered from a bloated treatment that accentuated its contrivances. Sprecher’s is a small film, but one whose modest grace provides greater satisfaction than most Hollywood blockbusters.