In 2002, 6-year-old Mason Evans, portrayed by Ellar Coltrane, navigates life alongside his divorced mother, Olivia (Patricia Arquette), and his 8-year-old sister, Samantha (Lorelei Linklater), in a quaint Texas town. While Mason shows a remarkable intelligence, he often finds himself distracted in school. His late homework submissions and attempts to sharpen rocks with a pencil sharpener mark his unconventional childhood. One day, he overhears a heated argument between Olivia and her boyfriend, Ted (Steven Chester Prince), revealing Olivia's struggles with the demands of parenting.
In 2003, seeking better opportunities, Olivia relocates the family to Houston to pursue her education at the University of Houston. Their new home, complete with a pool, offers Mason and Samantha their own rooms, yet sibling rivalry is rampant as the children frequently clash. With Olivia busy with her studies, their grandmother, Catherine (Libby Villari), steps in to help care for them.
The following year, Mason Sr. (Ethan Hawke) pays a visit to Houston and takes the siblings bowling, despite his uncertain future as he works in Alaska. The children observe a tense exchange between their parents as they watch from a window, illustrating the strain in their family dynamic. Olivia introduces Mason to her professor, Bill Welbrock (Marco Perella), and Mason notices an unexpected connection between them.
By 2005, a new chapter unfolds as Olivia and Bill marry and merge their families. While they honeymoon in Europe, the children spend quality time with their grandmother, engaging in activities like video games and attending a midnight Harry Potter release. Mason forms a bond with a girl named Nicole (Jessi Mechler), who harbors feelings for him.
In 2006, Mason Sr. strengthens his relationship with the kids during an adventurous outing, which includes a thrilling Astros game and quality time at his house. As Mason's father celebrates his milestones, Olivia juggles her education while trying to manage the strict household rules set by Bill, who maintains a regimental approach to parenting that includes chores for the children and enforcing haircuts for Mason.
However, the atmosphere shifts in 2007 as Bill's alcoholism turns abusive. Following a violent confrontation, Olivia courageously moves out with her children, sparking a new beginning as they struggle with the emotional toll. Samantha grapples with feelings of guilt over leaving her step-siblings behind, while Mason and Samantha must adapt to new schools, making fresh starts.
By 2008, conversations about teenage relationships arise, as Mason Sr. educates his children about contraception while they become involved in local political campaigns. He cultivates a deep connection with Mason through shared hobbies and life lessons, ultimately guiding him through the complexities of adolescence in their new home near Austin.
As the years progress into 2009 and beyond, Mason experiences the trials of teenage life, facing bullying, navigating romantic interests, and managing familial pressures stemming from his mother's career changes and personal relationships. Throughout high school, Mason's artistic talent is recognized, though his ambition wavers. A painful breakup with Sheena (Zoe Graham) coincides with a significant achievement in photography, marking a pivotal point in his young adulthood.
By 2013, as Mason finishes high school, he finds himself reflecting on his journey during a bittersweet graduation celebration with family. The impending transition to university brings mixed emotions for Olivia, who grapples with the rapid passage of time. As Mason embarks on his new adventure at Sul Ross State University, he encounters various new relationships, including those with his roommate, Dalton (Maximillian McNamara), and Nicole, with whom he shares profound discussions about life, encapsulating the poignant idea that “moments seize people.”
