Joe Swanberg wrote “Digging for Fire” with actor Jake Johnson, center, who stars as a Los Angeles high school teacher who happens upon a couple of buried artifacts that suggest a deeper mystery. (Ben Richardson/The Orchard)

For the past 10 years, ­writer-director Joe Swanberg has been perfecting his own way of making small-canvas, improvisational movies, developing a devoted following on the festival/art-house/on-demand circuit. One of his first films, “Hannah Takes the Stairs,” introduced a feral force of nature named Greta Gerwig to the world. In recent years, he’s gone from discovering stars to casting them in his low-key, lower-budget projects, which have included performances by Anna Kendrick, Olivia Wilde, Melanie Lynskey and Lena Dunham, among others.

If you’ve never seen a Swanberg film, “Digging for Fire” is a terrific place to start, offering a diverting, often amusing example of why actors love working with him so much. He gives them outlines rather than dialogue-heavy scripts, allowing them to find their way from the beginning to the end of each scene with their own intuitive resources; the result is a film that feels unforced and slightly suspenseful at the same time. You’re never entirely sure what’s around the next corner, but it’s usually funny, slightly mortifying and wistfully revealing.

Swanberg wrote “Digging for Fire” with actor Jake Johnson, who stars as Tim, a Los Angeles high school teacher married to a yoga instructor named Lee (Rosemarie DeWitt). When one of Lee’s Hollywood clients allows the couple to housesit while she’s off making a film, Tim and Lee move in with their 3-year-old (played by Swanberg’s preternaturally charismatic son, Jude). Poking around the property, Tim happens upon a couple of buried artifacts that suggest a deeper mystery beneath the underbrush. He wants to stage an amateur archeological dig, but Lee is having none of it.

When Lee decides to decamp with the kid for the weekend, the game is afoot. Tim immediately invites some buddies over for beers and hot dogs and, inevitably, some exploratory shovel work. Meanwhile, Lee concocts an excuse to have her own time away from domestic obligations, Ubering her way to Malibu for a night of aimless ad­ven­ture. “Digging for Fire” chronicles a youngish-oldish couple taking a break from parenthood, encroaching age and the sobering reality of a lifetime of monogamy. Tim’s desperate search for whatever it is he might find is clearly a sublimation of his own anxieties, desires and tightly controlled sexual curiosity.

These themes are nothing new. They’ve been just as smartly addressed in such recent films as “Afternoon Delight,” “The One I Love” and “The Overnight.” But because of Johnson and DeWitt’s nimble central performances — as well as the heaven-sent supporting cast — “Digging for Fire” feels improbably fresh and spontaneous. Sam Rockwell injects a note of borderline deranged volatility as one of Tim’s buddies (he’s barely recognizable under a bushy beard), while Orlando Bloom delivers a smooth turn as a seductive restaurant owner whom Lee meets. Meanwhile Mike Birbiglia steals almost every scene he’s in as one of Tim’s fellow teachers who’s concerned about his friend’s deteriorating psychological state.

Like Tim and Lee’s housesitting gig, “Digging for Fire” is a pleasant escape — an attractively shot, gracefully edited and, finally, emotionally satisfying mystery about the nature of marriage itself. It all comes down to what’s worth bringing up and what’s better off staying buried.

R. At Landmark’s E Street Cinema. Contains profanity including some sexual references, drug use
and brief graphic nudity.
83 minutes.