Cece is a warm, intelligent woman in her twenties who recently left medical school. She travels to Montana to prepare for her upcoming wedding to Charlie Margolis. She struggles with anxiety regarding her future and her choices. When she meets Charlie's best friend, Garrett, her predetermined path is challenged, and her story follows her quest to find personal fulfillment.

Charlie is an ambitious cardiac anesthesiologist devoted to his fiancée, Cece. He is highly protective of those he cares about, actively managing the details of his upcoming wedding. He shares an intense, long-standing bond with his college friend Garrett, whom he credits with saving his life during their youth.

Garrett is a Montana local and Charlie’s best friend from college. He works as a luggage handler and lives with depression triggered by the accidental death of his friend Elias. He is deeply critical of humanity's environmental impact. Initially skeptical of marriage, his perspective shifts when he is asked to officiate Charlie's wedding.

Jasper is Charlie's son, a boy whose life is shaped by a serious medical condition. As he grows into an adolescent, he becomes self-conscious about his medical device and struggles with his parents' separation. He turns to music but faces significant challenges with substance use, frequently pushing away his father's attempts to help.

Lana is a young woman raised in Salish, Montana. She observes the complex dynamics of the adults around her, developing a cynical view of traditional relationships. She eventually moves to Los Angeles to pursue an acting career, maintaining a complicated connection to Charlie's son, Jasper.

Elias is an older college student who forms a tight-knit trio with Charlie and Garrett. He is energetic and becomes a central figure in their early lives. His tragic death during a winter ski trip casts a long shadow over the surviving men.

Angeliki is Charlie's first wife and the mother of his two children. She integrates into Charlie's social circle and family life, eventually facing the dissolution of their marriage as Charlie continues to struggle with his past attachments.

Teá is Charlie and Angeliki's daughter and Jasper's sister. She spends summers at the lake and occasionally meddles in the lives of the older teenagers, creating minor disturbances during family gatherings.

Garrett's 57-year-old father lives with pulmonary fibrosis. He previously ended his marriage after coming out as gay. He serves as his son's primary social contact during a period of isolation, gently encouraging him to engage more with the world.

Jake is one of Charlie's brothers. He provides critical support during a difficult time in Charlie's life, actively helping his brother recover from heartbreak and introducing him to new social connections.

Brig is part of the original college friend group. As the men age, his health complications prompt the group to gather at the Margolis cottage, highlighting the physical vulnerabilities of their circle.

Soledad is Brig's wife. She assists him with his mobility challenges during summer gatherings and attempts to maintain a lighthearted social atmosphere for the group.

Bengt is Garrett's research partner. The two spend long hours together in remote Montana environments tracking endangered wolverines, forming a solid professional bond.

Sabina is a coveted student on their college campus. Her presence inadvertently helps cement the early friendship between Charlie and Garrett before tragedy strikes their group.

Becky is a woman Charlie dates later in his life. Her strong physical resemblance to Cece causes friction among the teenagers at the lake, and her relationship with Charlie faces significant turbulence.

Paige is Cece's best friend from high school. She travels to Montana to assist with wedding preparations, trying to soothe Cece's mounting anxiety by attributing her fears to typical nerves.

Gail is Cece's favorite author. She agrees to do a reading at an independent bookstore, but the event turns chaotic when she arrives during a severe storm to an impaired host.

Kayla is a friend of Cece's. She tries to help manage a disastrous author reading event, attempting to keep Cece functioning when an evening goes wrong.

Charlie's father travels to Montana for his son's wedding but quickly contracts norovirus. Despite his severe illness, he attempts to help set up chairs for the ceremony.

Charlie's mother travels to Montana for the wedding but falls victim to the sudden illness sweeping through the guests, forcing her to quarantine at a hotel.

Pranavi is Teá's friend. She accompanies her during summer trips to the lake and participates in adolescent mischief, including stealing a phone.