Thirteen-year-old Connor is the best friend of Branwell Zamborska. He lives with his parents and often visits his older half-sister, Margaret. When Branwell falls completely silent after being accused of a terrible crime, Connor creates a system of flash cards to communicate with him. He firmly believes in his friend's innocence and takes on the responsibility of figuring out what truly happened.

Thirteen-year-old Branwell is a bright, talkative, and eccentric boy who has suddenly gone completely mute. He resides in a juvenile detention center after being accused of harming his infant half-sister, Nikki. Struggling with complex feelings about his blended family, he relies entirely on eye blinks and flash cards to communicate with Connor.

Margaret is Connor's much older half-sister who runs a computer consulting business out of her home. Because she grew up in a blended family, she understands the feelings of displacement Branwell experiences when his father remarries. She provides Connor with a safe space to discuss his findings and actively helps him investigate the case.

Vivian is the twenty-year-old English au pair hired by the Zamborska family to care for baby Nikki. She presents herself as sophisticated and charming, often blurring the boundaries of her professional role. She claims that she awoke from a nap to find Branwell harming the baby, making her the primary witness in the investigation.

Morris is a tough-looking delivery driver with a mohawk, leather jacket, and piercings. He initially claims to know nothing about Branwell or the Zamborska family. He holds valuable information about the events leading up to Nikki's hospitalization.

Dr. Zamborska, often called Dr. Z, is Branwell's father and a researcher for the Genome Project. He carries lingering guilt from the car accident that killed his first wife. Desperate to help his son, he places immense trust in Connor's ability to reach Branwell.

Nikki is Branwell's infant half-sister, the daughter of Dr. Zamborska and Tina. Following a mysterious incident at the house, she is hospitalized in a coma, serving as the central catalyst for Branwell's silence and detention.

Tina is Dr. Zamborska's second wife and Nikki's mother. She works as a researcher for the Genome Project. She is fiercely protective of her newborn and maintains a somewhat strained, distant relationship with her stepson.

Yolanda is the house cleaner who works for both the Kane and Zamborska families. She observes the daily habits of the household staff and family members, maintaining a slow and steady approach to life.

Branwell's maternal grandparents live in Florida and maintain high, strict standards for behavior. They harbor a strong dislike for Dr. Zamborska and Tina, and they hire a lawyer in an attempt to force Branwell to speak.

Connor and Margaret's father works at the local university. He has a strained relationship with his older daughter, Margaret, stemming from his remarriage, but he uses his university connections to assist with the investigation.

Connor's mother is the second wife of Connor's father. She provides a stable home environment for Connor and attends family dinners, representing the successful blending of their family unit.