context: Darius Britt (Aubrey Plaza) is a disillusioned college graduate who lives at home with her widower father (Jeff Garlin) and interns at Seattle Magazine. One of the magazine's writers, Jeff Schwensen (Jake Johnson), proposes to investigate a newspaper classified ad that reads:[8]
  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.
  Jeff's story idea is approved by his boss, Bridget (Mary Lynn Rajskub). Jeff selects his team, made up of Darius and a man named Arnau (Karan Soni), the latter of whom is a studious biology major interning at the magazine to diversify his resume. They travel to the seaside community of Ocean View to find and profile the person behind the ad. Jeff later reveals an ulterior motive for this assignment: to track down a long-lost love interest who lives in town.
  Darius discovers that the person behind the ad is Kenneth Calloway (Mark Duplass), a stock clerk at a local grocery store. Jeff's attempt to approach Kenneth alienates him, so Jeff orders Darius to make contact. Darius' disaffected attitude serves her well, and she quickly endears herself to Kenneth as she poses as a candidate to accompany him on his mission. While Kenneth is paranoid and believes that "secret agents" are tracking his every move, Darius gains his trust as she participates in a series of training exercises in the woods around his house and begins to develop feelings for him. She tells Kenneth about the death of her mother when she was young and that her mission is to prevent it. Kenneth says his mission is to go back to 2001 and prevent the death of his old girlfriend Belinda, who was killed when someone drove a car into her house.
  Meanwhile, Jeff tracks down Liz (Jenica Bergere), his fling from his teenage years; although she is not as attractive as his memories of her younger self, they reconnect and sleep together. He asks her to come back with him to Seattle, but she believes this is just another fling for Jeff, so she refuses. Upset by her rejection, Jeff takes Arnau out on the town, and they pick up some young women. Jeff tells Arnau to not waste his youth and convinces him to spend the night with one of the women.
  The next morning, Jeff receives a phone call from Bridget, who has been following up the team's notes on the story; she informs him that Belinda (Kristen Bell) is still alive. During an interview, Darius learns Belinda was only friends with Kenneth and that Kenneth had driven into her then-boyfriend's house, but no one was injured. After the interview, Darius is questioned by two government agents who have been following Kenneth and believe that he may be a spy because of his communication with government scientists.
  Darius returns to Kenneth's house to confront him about Belinda, but Kenneth rationalizes that his time traveling must have worked. Jeff then comes in to warn them that the government agents are also on the property. Kenneth panics and runs into the woods. Darius follows him and finds Kenneth has boarded his time machine, which has been integrated into a small boat. Darius apologizes for lying to Kenneth, tells him everything else they shared was real, and joins him on the time machine. Kenneth tells Darius that his mission has been updated, saying he now wants to go back for her. As Jeff, Arnau and the two government agents watch, Kenneth activates the time machine and it disappears, along with him and Darius.
question: Whom did Kenneth wanted to prevent from dying?
answer: his old girlfriend Belinda