The film opens on a Suburban bedroom. Lights flicker on the ceiling. The protagonist, Ernest Gladwell, awakens to sees a women outside his window flickering a flashlight. He climbs out of his window into a rolling plume of violet fog. He emerges from the fog dressed in an oversized Mint Suit, dancing towards the woman. They hop into a White Mercedes convertible and start the engine. Ernest leans in the kiss the woman, but his advance is abruptly cut short by a morning alarm, revealing the sequence to be a dream.

The camera pans around Ernest's room showcasing various academic accolades interspersed with posters of New Wave bands and cassette recorders. Ernest hurriedly slips on a uniform and rushes down to the kitchen. As Ernest enters the kitchen, he breaks the fourth wall and freezes time. The camera tracks with Ernest as he saunters around his motionless family describing his life in Violet Heights. Ernest informs the audience that he’s 19, lives at home with his parents and works as a Valet at the “Violet Heights Social Club”. He reveals that he was his High School Valedictorian, but opted not to attend college and now spends his days recording music in his bedroom. He jokingly describes himself as “The spitting image of wasted potential”.

Ernest drives a decrepit 1978 Saab Hatchback to the Country Club.  As he arrives, he greets his co-worker and best friend Graham Krumpels - a fast-talking, gawkish kid with thick glasses. Graham informs Ernest that their High School classmates have returned from College for the summer and are gathering for a raucous pool party that evening. After some cajoling, Graham convinces Ernest to join him at the party. Throughout the day, patrons of the Country Club are introduced as Ernest and Graham park their vehicles. Patty Weinstock, a wealthy recent divorcee, immodestly flirts with Graham as he parks her car. She regularly jokes that “anything he asks for is as good as his”. As Ernest and Graham’s shift ends, they are struck by a drive-by-egging, orchestrated by Rich Weinstock, Patty's son and former star High School Linebacker. As he pulls out of the parking lot, Rich exclaims “Glad to see you freaks are both sticking around The Heights! We’ve got a fun little surprise for if you're dumb enough to show up to the party later!”

Defiantly, Ernest and Graham attend the party. Ernest spots his high school sweetheart, Amelia Hartford, poolside. We recognize her to be the woman from Scene 1.  Amelia and Ernest broke up last fall, when she left to attend college at USC. She is now dating Rich. Ernest has a brief, nervous conversation with Amelia before Rich interrupts. Afterwards, Ernest slips into another surreal reverie, imagining Amelia in the pool with synchronized swimmers dancing around her. His daydream is suddenly disrupted by the blast of M80s from the bushes immediately behind him and Graham. While disoriented by the blast, Rich and his cronies push them into the pool. From the water, Ernest vaguely discerns Amelia lambasting Rich. Amelia apologetically helps Ernest and Graham out of the pool and offers to give them a ride home. On their way back, the trio stops at a diner. At the diner, the former friends reconnect and rekindle their relationship. When Amelia drops Ernest off at home she admits that she misses him and asks him to call her in the future - "as friends".

Emotionally distraught by his separation from Amelia, the impending departure of Graham, and his failed attempt to connect with Robert Smith, Ernest enters a panic attack. In his despondent state, Ernest accidentally overdoses on anxiety medications. As he loses consciousness, he blasts his stereo system at full volume to call for help.

The next day, Ernest awakens at the hospital with Amelia, Graham, and his family at his bedside. After a tearful embrace, they explain to Ernest that his sister Evelyn found him and called for help - if another 15 minutes passed he would have died. After an emotional conversation explaining what happened, Ernest’s visitors leave him to rest. On the way out of the door, Amelia stops to ask Ernest about the music playing in his room. Amelia pulls a purple tape out of his pocket and asks if it was Ernest’s music. Ernest confirms that it was. She had listened to it in the waiting room on repeat for the last 12 hours. Awe-struck, she abashedly probes "well, whoever you're singing about must be pretty special". He replies "if only she knew how he felt about her". They kiss. Amelia exits, beaming.

A few days after, Ernest is back in his bedroom. After reflecting on events of the past weeks, he decides to enter the next chapter of his life by committing to the University of Minnesota in the fall, As he presses pen to paper to commit, Ernest receives a call. It’s Robert Smith. He invites Ernest out to LA, and tells Ernest he thinks he can get his record made. Ernest puts the pen down and wildly celebrates around his room. He informs Graham and his family immediately.

Afterwards, he goes to Amelia’s, but he is informed by her Father that she has gone back to USC for the summer to work on campus. Downtrodden, he calls her at her dorm. He learns that she’s broken up with Rich and didn’t feel safe at home any longer. Saddened but understanding, Ernest mentions that he is going to be in LA soon. He informs Amelia of his breakthrough with Robert Smith. They make plans to meet up as soon as he arrives.

Just as Ernest is about to leave in his Saab, Graham pulls up in a White Mercedes Convertible. He recalls Patty Weinstock’s earlier offer that “anything he asks for is as good as his”. He offers the car to Ernest saying “You’re going to need a cooler car, if you’re going to be a rock star”. Tearfully, the friends embrace and say goodbye.

The movie ends with Ernest driving along the Pacific Coast Highway in his new car, dressed in a Mint Suit, arm around Amelia.