There’s a long movie tradition of likable but apparently cuckoo people whose presumed psychoses turn out to be at least arguably genuine. There was Elwood P. Dowd, for example, whose best friend was an invisible six-foot rabbit named “Harvey.” And Justin Playfair, whose delusion that he’s Sherlock Holmes was amiably treated in “They Might Be Giants.”

The latest addition to this roster is Kenneth (Mark Duplass), a fellow who not only believes he’s invented a time machine but advertises for someone to join him in a trip to the past. It’s that invitation that starts the plot rolling: Jeff (Jake Johnson), a cynical reporter at a Seattle magazine, pitches an idea about tracking down the guy and writing up his story. Soon he’s off to the small town of Ocean View, where the return PO Box is located, with interns Darius (Aubrey Plaza) and Arnau (Karan Soni) in tow.

They identify the fellow fairly easily, but when Jeff approaches him, Kenneth turns him down flat. That’s okay with Jeff, who’s really come to Ocean View to look up his old high school flame (Jenica Bergere) and happily turns over the investigative side of things to Darius, who quickly establishes a rapport with Kenneth and finds herself—of course—sympathizing with, and actually believing in, him. Though the path isn’t without hurdles, it’s not surprising that in the end she’s willing to make a leap of faith and join in his presumably crazy plan.

“Safety Not Guaranteed”—the phrase comes from the classified that Kenneth’s placed in the magazine to recruit a partner—isn’t terribly well-crafted from a narrative perspective. (Kenneth, for example, has apparently gone to great lengths to preserve anonymity, keeping his street address secret because he’s convinced government types are out to get him; but he seems unsurprised when both Jeff and Darius show up in response to his ad.) But it has a loopy, lackadaisical charm that makes up for the script’s untidiness and what looks to have been a very modest budget.

That’s largely due to Colin Trevorrow’s easygoing direction, which allows for the quirkiness to register without italicizing it (a notable example being Kenneth’s nighttime raid on a nearby medical company for equipment, which is beautifully staged) and to his excellent cast. Duplass makes an attractively oddball protagonist, intense but not scary, and Plaza’s deadpan moroseness matches up beautifully with his juvenile enthusiasm. Even more importantly, Johnson makes Jake—who might have been just an annoying womanizer—into a genuinely amusing guy with regrets of his own, whose dalliance with his erstwhile girlfriend takes on surprising depth, acting as a nice complement to the Kenneth-Darius relationship while reemphasizing the film’s overall idea that love is worth working for. (It certainly helps that writer Derek Connolly has provided Jake with many of the script’s best lines; but they wouldn’t sound nearly as good were Johnson not delivering them with such adept throwaway timing.) And one shouldn’t neglect Soni, whose delightful turn as the dour, inexperienced nerd drawn out of his shell on an incident-filled road trip has a touch of the old John Hughes formula to it.

“Safety Not Guaranteed” is obviously a small production, and the limitations sometimes show in Benjamin Kasulka’s widescreen cinematography. Overall, though, it’s pleasant to watch, ending with a bang that proves that inventive filmmakers can still make a visual splash with very limited resources. And as edited by Franklin Peterson and Joe Landauer to a crisp eighty-four minutes, it doesn’t overstay its welcome, not lingering to allow the whimsy to curdle. If safety isn’t guaranteed by the film’s title, a viewer’s satisfaction with this genial, warm-hearted movie pretty much can be.