Sophie is a horticulturist experiencing professional burnout who takes a temporary summer position restoring the deteriorating grounds of Lilymoor. She struggles with intense survivor's guilt following the death of her best friend, Harriett, taking the job primarily to fulfill a decade-old promise they made to return to the estate. Her scientifically grounded worldview faces a challenge when she discovers a magical blue door that appears only at golden hour, leading to a secret, unfinished garden.

Eula's great-nephew is a successful lawyer who appears trapped in a perpetual sunset within a magical garden at Lilymoor. Following a tragic greenhouse fire during his teenage years, he accepted sole responsibility for the incident and distanced himself from his family and the estate. Though initially abrasive and cold, his time in the garden reveals a passionate, horticulturally skilled man who fears his past mistakes define him.

Sophie's deceased best friend was an aspiring novelist who died of cancer a year before the main events of the story. She possessed a deep curiosity for the world, collecting untranslatable words that she shared with Sophie. Her belief in everyday magic and romance heavily influences Sophie's understanding of Lilymoor and her own grief.

Eula's great-nephew is the head of a prestigious architecture firm who arrives at Lilymoor concerned about his aunt's sudden retirement plans. While he projects a carefree and charming exterior, he feels deep guilt regarding Eula's recent fall and the destruction of the greenhouse years ago. He fears the responsibility of inheriting Lilymoor alone but refuses to abandon the estate entirely.

The eccentric, independent matriarch of Lilymoor is preparing to retire and announce her successor at the upcoming bicentennial party. Having grieved her late husband Henry for over sixteen years, she has allowed much of the estate to deteriorate rather than face the spaces associated with his memory. She hopes her retirement will force her estranged great-nephews to reconcile.

The meticulous events coordinator at Lilymoor is tasked with organizing the massive bicentennial celebration on a severely shortened timeline. Outspoken and frequently overwhelmed by her responsibilities, she deals with unreliable vendors and a chaotic dating life. She quickly forms a supportive friendship with Sophie, helping draw the horticulturist out of her shell.

The affable handyman and groundskeeper at Lilymoor provides crucial emotional support and comic relief to the estate staff. He briefly attended Yale before realizing he preferred a simpler life working with his hands and playing music. He acts as a comforting presence for Sophie, offering practical wisdom when she struggles with her work or her sorrow.

Eula's late husband designed many of Lilymoor's intricate gardens before his death sixteen years ago. A visionary who believed strongly in the magic of unrealized dreams, he left behind water-damaged journals containing plans for a special garden intended as a gift for his wife.

The highly territorial resident goose at Lilymoor frequently menaces the staff and visitors. Rescued as a young bird by Cyrus, the goose acts as a constant, chaotic force on the grounds, requiring the staff to constantly remain on guard.