In his feature directing debut, “Safety Not Guaranteed,” Colin Trevorrow manages the tricky feat of moving subtly and seamlessly between several different genres within a relatively short period of time.

With a low-budget intimacy, his film begins life as an oddball road-trip comedy then turns unexpectedly romantic before becoming a genuinely paranoid, sci-fi thriller. It also provides as welcome showcase for Aubrey Plaza in a rare leading role as Darius, a sullen intern at a Seattle magazine who becomes the reluctant participant in a pseudo-journalistic investigation.

In films such as “Funny People” and in the TV series “Parks and Recreation,” Plaza has honed a dryly sarcastic, cool-girl persona; it’s a pleasure to see her soften and show some vulnerability here.

The clever premise from screenwriter Derek Connolly finds Darius and two of her co-workers — cynical reporter Jeff (Jake Johnson) and fellow intern Arnau (Karan Soni) — traveling to find the person who placed an intriguing classified ad. “Wanted: Someone to go back in time with me. This is not a joke,” it reads in part. “Must bring your own weapons. Safety not guaranteed.”

They track down Kenneth (Mark Duplass), a loner grocery store clerk, in a small, coastal Washington town, then try to infiltrate his life and get to the bottom of his bizarre story. What’s lovely is that while Kenneth is a misfit and more than a little out there, the movie never makes fun of him. Well, the mullet and the jean jacket are played for kitschy laughs, but Duplass brings an earnestness and a sweetness to the character that make him surprisingly complex and compelling.

Darius flirts with Kenneth and makes him think she’s completely along for the ride, adopting his hilarious self-serious manner of speaking with phrases like “There no sense in nonsense when the heat’s hot.” But as she gets to know him through break-ins to steal equipment and target practice in the woods, she eventually finds herself warming up to him, perhaps for the first time ever. In the film’s most charming scene, in which Kenneth serenades her by the campfire — and Duplass really can sing — it’s finally obvious to us what she sees in him.

Meanwhile, Jeff spends his days drinking at the local dive bar and trying to hook up with an old fling from his youth; the scene-stealing, wisecracking Johnson makes this inherently shallow, selfish character work. As both he and Darius get sucked deeper into these newly forged relationships, the quiet, nerdy Arnau consistently serves as the voice of reason — but he’ll also undergo a transformation he didn’t expect.

Together, the three mismatched co-workers share an easy, teasing banter that gives their journey real buoyancy.

"Safety Not Guaranteed" is rated R and is showing at the State Theatre.