On a sun-soaked afternoon, 18-year-old Elliott (Maisy Stella) sets off on a birthday boating escapade with her closest friends, Ruthie (Maddie Ziegler) and Ro (Kerrice Brooks). While her family—consisting of her mother Kathy (Maria Dizzia), father Tom (Alain Goulem), and brothers Max (Seth Isaac Johnson) and Spencer (Carter Trozzolo)—eagerly await her return for a celebratory cake, Elliott makes a spontaneous decision to prolong the festivities with her friends by camping under the stars. This unexpected adventure leads to a serendipitous encounter with Chelsea (Alexandria Rivera), the local barista who captures Elliott's heart, paving the way for a night filled with intimacy and connection.
In search of deeper experiences, the trio acquires psychedelic mushrooms from Ro's cousin, preparing them into a potent tea that ignites a surreal exploration of their minds. As the effects start to unfold, they are swept into a euphoric realm filled with whimsical movements and laughter. While Ruthie and Ro become immersed in their own enchanting world, Elliott finds herself captivated by an older woman—Older Elliott (Aubrey Plaza)—who reveals herself as Elliott's future self. Marked by a notable scar from her childhood, she shares Elliott's unique physical traits, leaving young Elliott both skeptical and fascinated by this mystical encounter.
With curiosity piqued, Elliott eagerly questions her older self about the future that lies in wait. “You’re gonna be almost forty, and you’ll be working in medicine,” Older Elliott reveals, much to young Elliott's dismay, as it starkly contrasts her current carefree visions. An impulsive moment leads to a shared kiss, bridging their connection across time and generations.
Imparting sage advice, Older Elliott emphasizes the importance of cherishing family bonds and the love of their parents while cautioning her younger counterpart about a man named Chad. The weight of this warning looms over Elliott's romantic aspirations, and as exhaustion sets in, they drift into a peaceful slumber.
As dawn breaks, casting shades of rose and gold across the sky, Elliott returns home with Ruthie and Ro. The initial detachment she felt from her mother, Kathy, softens upon realizing she has missed out on the celebratory cake, a poignant reminder of familial ties. Drawn back to Chelsea's magnetic presence, Elliott seeks another intimate encounter on the serene lake, their bodies entwined in a tapestry of shared desire.
However, the reality of summer responsibilities tugs at her, as her brother Spencer arrives to rouse her from sleep, reminding her of the chores awaiting. Later, in a moment of liberation, Elliott dives into the cool lake waters for a refreshing swim, only to cross paths with a charming young man, Chad (Percy Hynes White). His playful charm disarms her, but the moment he introduces himself as Chad sends a wave of panic coursing through Elliott, shattering her newfound calm. Frantically, she swims away, heart racing.
In her quest for clarity, Elliott reaches out to Older Elliott via her phone, finding a contact labeled “MY OLD ASS”. As she sends a trembling message detailing her encounter with Chad, the urgent response reinforces Older Elliott's warning: stay away from him. Intrigued and persistent, Elliott calls the enigmatic number again, hearing her future self's voice weave cryptic advice about avoiding Chad.
Undeterred by the warnings, Elliott finds herself drawn back to the lake, encountering Chad once more. His charm brings laughter, yet doubt nudges her away again. With each failed attempt to reconnect with her older self, the silence weighs heavily on her until she seeks comfort in her familial relationships, spending meaningful time with her brothers and indulging in shared passions.
However, the unexpected arrival of Chad at breakfast adds tension to the delicate family dynamic. Amid awkward interactions, Elliott tries to escape by suggesting a golf outing with Max, but Max innocently invites Chad along, complicating her plans further. As they navigate the course, Max reveals his parents' intentions to sell the farm, invoking strong feelings of nostalgia in Elliott, who confides in Tom about her emotional connection to the land.
During a tranquil boat ride, Elliott shares her worries with Chad, who offers thoughtful insights. Their vulnerable exchange brings them closer, leading to a spontaneous kiss that sends Elliott into a spiral of self-doubt, prompting her to retreat once more.
In search of guidance from her older self, Elliott encounters an unsettling silence. Feeling lost, she turns to Ro for the remaining psychedelic mushrooms, embarking on a solitary journey through the woods that merges reality with vibrant hallucination. In a whimsical vision, she imagines serenading Chad as Justin Bieber, complete with symbolic gestures that reflect her youth.
Moments of tenderness with Kathy on the porch rekindle Elliott's sense of familial love, reminding her of cherished memories. The following morning, she confides in Ro about her feelings for Chad, contemplating her own sexuality. Eager to introduce Chad to her friends, she leads Ro and Ruthie to the docks, where she shares a boat ride with Chad. Their laughter fills the air, yet an accident causes the boat motor to detach, spilling into the water, only to further fortify their bond.
As the afternoon unfolds, Elliott confesses her feelings for Chad—despite the warnings—deepening their connection. They find themselves once again intertwining, their budding romance flourishing. This heartfelt moment is abruptly interrupted by the emergence of Older Elliott from the trees, unveiling the consequences of their choices. Sharing her own history with Chad, she speaks of longing and loss, revealing his tragic fate that looms over their relationship. Young Elliott, defiant yet apprehensive, decides to embrace their love story, undeterred by the uncertainties that lie ahead.
The film culminates with Elliott navigating the emotional complexities of love and family, sealed with a tender kiss with Chad on their idyllic lake. As Elliott embarks on one last enchanting boat ride, she embraces the poignant journey of her youth, stepping boldly into a future shaped by love, loss, and discovery.
