The tapestry of Sybil at Sixteen is intricately woven with themes of familial bonds, love's complexities, deception, and the trials of living with disability and facing mortality. At its heart is Sybil, the central figure whose narrative unveils critical events from the past, guiding readers through a landscape shaped by both her virtues and flaws. Initially, Sybil is portrayed as an all-loving daughter, blind to her father’s imperfections. Her journey is one of transformation, evolving into someone who perceives her father's true nature while still holding him dear. Her deep affection for him drives her to become an accomplice in his financial schemes, driven by a gratitude amplified by the sacrifices her family made following her accident—even as her love for her sisters, particularly Claire, remains secondary to her devotion to her father.

Nick Sebastian, Sybil’s father, grapples with the frustration of not being able to support his family as he wishes. He is especially tormented by Sybil’s suffering, though his ability to ease her pain is limited.

Meg, affectionately called "Megs" by her daughters and "Daisy" by Nick, is the family's cornerstone. Her inheritance checks and job provide a stable income. Raised in affluence, she had chances to marry into wealth and status, but her heart led her to Nick instead. With compassion and insight, Meg cares for her family, though her heart often weighs heavy with worries about Nick and her daughters.

Claire, Sybil's immediate elder, is graced with striking beauty and shares her father's knack for cunning and strategy. A model flourishing in New York, Claire maintains a protective fondness for Sybil despite her generally detached demeanor towards her family. Her past includes a dissolved marriage, originally intended for Thea, netting her $50,000 through her cleverness. This windfall not only aided Sybil but also propelled Claire's career in modeling, making her the only sister with significant earnings.

Thea, second in age among the sisters, also resides in New York. Past grievances have created distance between her and Claire. Thea, inheriting her mother’s blonde beauty, aspires to a medical career, distinguishing her future ambitions.

Evvie, the eldest sister, anchors the family but shares a distant relationship with Sybil, having left for college when Sybil was just twelve. Evvie is romantically involved with Sam Steinmetz Greene, with marriage plans on the horizon, yet this relationship further isolates her from her family. Sam harbors a secret he keeps from Evvie’s kin.

As the story of Sybil at Sixteen unfolds, these central characters navigate a chaotic sea of emotions—love, care, suspicion, and even animosity—as pivotal events unravel. They endure deep sorrow and anguish as they confront the deaths of two beloved family members.

Other figures flit through the narrative, their roles brief yet crucial to the story’s cohesion and resolution. Sam, devoted to Evvie, finds his loyalty tested when a crisis shifts his priorities to his own family. Though absent, Linda Steinmetz, Sam's mother, subtly influences the plot. Meanwhile, Clark, a man of wealth and stability, remains a steadfast ally to the Sebastian family, despite Meg choosing Nick over him.