It’s often been said that today’s best comedy writers either work for The Onion, The Daily Show, or McSweeney’s. But this isn’t entirely true. They also sometimes write for the Craigslist’s classified section. For every seemingly “normal” Craigslist ad describing, say, a room for rent or a couch for sale, you’ll find at least two more that are certifiably insane—ads placed by elderly women looking to rent out their bathrooms or by young men looking for “moustache mentors.” A brief scroll through the website is often the equivalent of at least 10 network sitcoms.

So it’s no surprise that, in an age where movies are based on board games and children’s toys, someone decided base a movie off a Craigslist ad. What is somewhat surprising is that the source material proves to be just as entertaining in movie format as it is in html. For awhile, it looked like Men in Black III would be the summer’s best time travel comedy, but Safety Not Guaranteed easily surpasses it.

In the offices of an alt Seattle weekly that bears a striking resemblance to The Stranger, a jaded report (Jake M. Johnson) is sent to a Washington state coastal town to do a profile piece on the man who placed the following ad in the personal section: “Wanted: Someone to go back in time with me. This is not a joke. You get paid after we get back. Must bring your own weapons. Safety not guaranteed.”

He is assigned two interns, the grumpy Darius (Aubrey Plaza) who is still haunted by the death of her mother ten years prior, and the nerdy Arnau (Karan Soni). They soon discover that the ad was placed by Kenneth (Mark Duplass), an eccentric home hardware employee with a long history of breaking into medical research centers and nuclear power plants. After a horribly bungled initial encounter, it quickly becomes apparent the reporter is using the trip out of town as a pretext to visit an old high school flame, and so it falls to Darius to strike up a relationship with the time traveller and figure out what his deal is.

As she demonstrated on Parks and Recreations, Aubrey Plaza is very good at playing a grumpy intern. But the character is a bit too 0ne-note to sustain a feature-length film, and so director Colin Trevorrow and writer Derek Connolly wisely focus their attention on the reporter’s less outlandish attempts at undoing the mistakes of his own past. In 21 Jump Street, Jake M. Johnson had a very amusing scene as the high school principal. Here, he delivers on the promise of 21 Jump Street and gives a performance that should catapult him into the front ranks of comedic actors.

Although frequently very funny, Safety Not Guaranteed is, at its core, a serious movie about living with regret. It would make a great double bill with Another Earth, a movie which uses the prospect of visiting a parallel Earth rather than time travel as a way of dealing with characters haunted by the legacy of the past.

It’s become something of a cliché for indie movies to conclude on an ambiguous note. Last year alone, Meek’s Cutoff, Martha Marcy May Marlene, Bellflower, and (appropriately enough) Another Earth all frustrated audiences with the shocking abruptness of their end credit sequences. The ending of Safety Not Guaranteed perfectly demonstrates why this cliché is sometimes necessary. Throughout the movie, we’re left uncertain as to whether or not Kenneth has actually figured out how to go back in time. In the final 30 seconds, we’re provided with an answer—and it defies credulity. Had the movie ended 30 seconds earlier, it could’ve been just about perfect. Instead, what we get is the indie equivalent of Saving Private Ryan—a near perfect movie with a “Eh, they didn’t really need to go there” ending.