Isabel is a college freshman wrapping up her first year at Finch University. She looks forward to a summer at Cousins Beach with her boyfriend. She carries a deep attachment to the beach house and the Fisher family, having spent her childhood summers there. She makes decisions based on her heart and struggles to balance her current relationship with memories of her past.

Conrad is the older Fisher brother and a student at Stanford University. He carries the heavy emotional burden of his mother's recent death. He struggles with expressing his feelings openly and distances himself from those he cares about to protect them from his own grief. He is observant and quietly protective.

Jeremiah is the younger Fisher brother and Isabel's current boyfriend, attending Finch University alongside her. He is highly outgoing and heavily involved in his college fraternity. He seeks a fun, carefree life but faces challenges when his impulsive actions threaten his long-standing relationship.

Laurel is Isabel and Steven's mother, a woman with strong opinions and firm boundaries. She deeply misses her late best friend, Susannah Fisher. She tries to guide her children according to what she believes is best for them. She refuses to support decisions she views as premature or foolish.

Susannah is the late mother of Conrad and Jeremiah. Although she passed away from cancer before the events of the current summer, her memory heavily influences the actions and emotional states of both the Fisher and Conklin families. She left letters for her sons to open on their wedding days.

Adam is the father of Conrad and Jeremiah. Following the death of his wife, he attempts to maintain authority over his sons but struggles with a strained relationship, particularly with his older son. He employs his younger son as an intern at his company.

Steven is Isabel's older brother. He provides a grounded, fraternal perspective on the events unfolding around him. He often mediates or observes the ongoing dynamics between his sister and the Fisher brothers with a mix of sibling teasing and genuine concern.

Taylor is Isabel's childhood best friend who attends a different university. She is outspoken and fiercely loyal. She is quick to defend her friend against any perceived slights. She embraces college life enthusiastically and encourages Isabel to demand exactly what she wants out of life.

Anika is Isabel's college friend and intended sophomore-year roommate. She offers a sensible, outside perspective on Isabel's life and challenges her to think critically about her relationships.

Lacie is a sorority girl at Finch University who attends parties with Jeremiah's fraternity. She is outgoing and becomes a source of significant conflict in Isabel's life due to events that occurred during a spring break trip to Cabo.

Mr. Conklin is Isabel and Steven's father. He is practical and mindful of finances, treating his daughter to meals while remaining largely unaware of the complex emotional dynamics happening in her life.

Ernie is Conrad's former boss who used to own a local restaurant before his nephew took over. He serves as an older confidant for Conrad, offering blunt advice about life and romance based on his own long marriage.

Agnes is an intelligent student at Stanford who briefly dates Conrad. She recognizes his emotional unavailability and prompts him to reflect on his past feelings and capacity for love.

Denise is Adam Fisher's assistant. She is efficient and task-oriented, stepping in to handle organizational details for the Fisher family events.

John is Ernie's nephew who took over the local restaurant, demoting his uncle in the process. He occasionally mows his uncle's lawn to maintain family ties.

Elizabeth is Ernie's late wife. Her enduring connection with Ernie serves as an example of lifelong love for Conrad to consider.