Darius Britt, portrayed by Aubrey Plaza, is a disenchanted college graduate living at home with her widowed father while interning at a Seattle magazine. One day, one of the magazine's writers, Jake M. Johnson, comes across a peculiar newspaper classified ad that reads:
> "Wanted: Somebody to go back in time with me. This is not a joke. P.O. Box 91 Ocean View, WA 99393. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before."
Intrigued, Jeff pitches the idea to his boss, Bridget, and brings Darius along with Arnau, a diligent biology major played by Karan Soni, who is looking to enhance his resume. Together, they venture to Ocean View, hoping to profile the enigmatic person behind the unusual ad, while Jeff secretly aims to reconnect with a long-lost love from the area.
Their investigation leads them to Kenneth Calloway, portrayed by Mark Duplass, a grocery store stock clerk. However, when Jeff attempts to reach out to Kenneth, his approach backfires and causes a rift. Consequently, Jeff instructs Darius to establish contact instead. With her nonchalant demeanor, Darius wins over Kenneth, who is convinced that "secret agents" are monitoring him. As they engage in various training exercises in the wilderness, Darius finds herself developing feelings for Kenneth. A pivotal moment occurs when they share a kiss, revealing the depths of their bond.
During their conversations, Darius opens up to Kenneth about the tragic loss of her mother, expressing her desire to prevent such grief in the future. Kenneth, on the other hand, reveals his mission to return to 2001 to save his former girlfriend Belinda, who tragically died when a car crashed into her house.
Meanwhile, Jeff's hunt for Liz, played by Jenica Bergere, his high school crush, leads to a bittersweet reconnection. Although Liz seems different from Jeff's fond memories, he invites her to Seattle. She, however, declines, perceiving his intentions as superficial. Disheartened, Jeff seeks to distract himself by going out with Arnau, trying to make the most of their youth.
The situation takes a turn when Jeff learns from Bridget that Belinda is very much alive. When Darius interviews Belinda, she clarifies her past with Kenneth, denying any romantic involvement; while there were indeed no injuries, Kenneth had accidentally driven into her then-boyfriend's house. This revelation brings about a confrontation with two government agents who have been monitoring Kenneth, suspecting he might be a spy due to his mysterious communications.
Returning to Kenneth's home to confront him about Belinda, Darius finds him in a state of anxiety, claiming that Belinda's survival indicates his time travel was successful. Just then, Jeff burst in, cautioning them about the agents lurking nearby. In a panic, Kenneth assumes Darius is in league with Jeff, leading him to flee into the woods. Darius pursues him and discovers Kenneth actively working on his time machine aboard a boat.
In a heartfelt moment, Darius confesses her dishonesty but insists that their emotional connection was genuine. She decides to join Kenneth on this daring adventure. Kenneth recalibrates his mission, now intent on returning not just to change the past but to go back specifically for Darius. As the situation escalates, with Jeff, Arnau, and the agents watching from afar, Kenneth activates the time machine, making both Darius and Kenneth vanish into thin air, embarking on an uncertain journey through time.
