High school senior Walter Gibson and his best friend Lance are in high spirits as they prepare to embark on their college journeys. However, Walter is consumed by the realization that he has forgotten how to interact with women. As Lance heads off to UCLA, Walter transitions to a college in New England. Despite their efforts to maintain their friendship through letters, Walter's romantic luck continues to plummet. In an ill-fated attempt to attract the attention of the ambitious and introspective Alison Bradbury, he devises a plan to trick her into tutoring him. Unfortunately, this only serves to frustrate and distance her further.
One day, Walter receives an unexpected phone call from Lance, who invites him to California for Christmas break, promising that he has arranged a meeting with a beautiful girl, declaring her a "sure thing." Eager for a change in fortune, Walter finds a ride through a ride-share board with Gary Cooper and Mary Ann Webster. However, his trip takes an unfortunate turn when he discovers that he will be sitting next to Alison, who is heading to UCLA to see her boyfriend, Jason.
As the tension escalates between Walter and Alison, their bickering frustrates Cooper, leading him to abandon them on a deserted road, leaving an infuriated Alison behind. When Alison hitches a ride with a middle-aged man who makes unwelcome advances, Walter arrives just in time to rescue her. The two decide to stick together, trying to navigate their way to a train station.
However, the situation grows dire when Walter realizes he lacks the funds to cover bus fare, forcing them to seek refuge in a motel. Jealous after overhearing Alison chatting with Jason, Walter drowns his sorrows at a local bar, where he drunkenly joins in a round of Christmas carols. The following morning, in a bid to secure a ride, Walter hurries Alison out of their motel, even suggesting she stuff her shirt with scarves to mimic a pregnancy, hoping for better luck with hitchhikers.
Despite their efforts, they find themselves caught in a rainstorm until Alison recalls her father's emergency credit card. They use it to spend a luxurious night at an upscale hotel, indulging in drinks and dinner. The next morning, Alison feels a touch of warmth as she finds Walter holding her, but that comfort quickly fades as he distances himself upon waking up.
As they continue their journey through Arizona hitchhiking with a truck driver, Alison overhears Walter share his intentions of meeting his "sure thing." When they finally reach UCLA, Alison seethes in anger as she parts ways with Walter. Meanwhile, Walter arrives at a Christmas mixer where Lance has arranged for him to meet the anticipated girl. Alison, feeling listless at Jason's place, decides to join the same party with him.
The air is thick with unresolved feelings as Alison and Walter confront their jealousy. Walter attempts to engage with his "sure thing," but his thoughts remain preoccupied with Alison. Returning to campus after the break, the tension between them is palpable. During English class, Professor Taub reads aloud an essay by Walter that recounts his night with the "sure thing." The essay reveals profound truths as the protagonist grapples with love, causing Alison to realize the depth of their connection. After confessing her breakup with Jason, a passionate kiss unfolds between the two, leaving their futures uncertain yet hopeful.
