Summer Greenwood: The story's main protagonist. A rebellious, quick-witted, yet often socially awkward fifteen-year-old who lives alone with her two sisters (Lily and Tory) after her parents abandoned her in the Slump. Taken by Making Perfect as a test subject for their illegal experiments, she fights to survive and return to her family. 

Tyler Evans:  Summer's childhood best friend. His parents were scientists just like Summer's. They grew up together, and got abandoned in the Slump at practically the exact same time. He is taken alongside her by Making Perfect. Brave and tragically faithful, he acts as the brother Summer never had, watching her back as they fight to survive Making Perfect. 

Kace Foster:  Head official at Making Perfect. Captured by the corporation at a very young age, he grew up in the facilities before eventually being promoted to a guard. He climbed up the ranks quickly and at only twenty-one, is now one of Ian Cooper's most trusted advisors. Despite his upbringing, Kace despises everything that Making Perfect stands for. 

Blayze Galloway: A chestnut-haired, doe-eyed boy in Summer's unit that she immediately forms a partnership with. Throughout the book, their friendship strengthens, and he quickly becomes someone she can trust. Funny, loyal, and often just plain stupid, Blayze slowly sneaks into Summer's heart. 

Ocean: Summer's first friend, and roommate, in Making Perfect. She catches onto the budding friendship between Blayze and Summer almost immediately, teasing Summer about it relentlessly throughout the book. 

Lily Greenwood:  Summer's youngest sister. The goofiest of the three, she always tries to keep a smile on Summer and Tory's faces. When Summer is captured, she has to step up to take care of Tory, toughening her up and introducing her to the world Summer had always tried to protect her from. 
Tory (Victoria) Greenwood: The oldest Greenwood sister. She acts as the mother figure to Summer and Lily. But when she contracts Red Pox and is confined to her bed, Lily and Summer have to take care of her. 

Flame (Abigail) Steele: Blayze's adopted sister, and the only person Blayze can say he truly loves. Firey, tortured and angry, she cannot contain her hate for Making Perfect and the world she lives in. She has it out for Summer throughout the book and loathes her developing friendship with Blayze. 

Ian Cooper: The tortured son of Making Perfect's CEO. At the beginning of the book, although he comes off as brutal, he still remains ignorant of Making Perfect's ultimate goal. His sister is the only person he loves. When Summer first arrives at the facility, he is struck by her rebellious attitude and outspokenness. When he saves her from the guards after she breaks into the lab, it is shown that Cooper isn't as much of a monster as he's made out to be. Every action he takes is constantly driven by his desire to protect the one person he loves, but that motivation turns him into the one person he never wanted to be: his father.

Elle Cooper: Ian's little sister. She contracted a debilitating illness that had been slowly killing her since she was young. When it is announced that her treatment is failing, and that she is going to die, Ian denies it, desperately searching for the cure. 

Michael Cooper: The CEO of Making Perfect. Hard-willed father of Ian and Elle.

Aaron Steele: The leader of Troop 5, the Slump's resistance group. Flame's older brother, him and his sister took in orphan Blayze after his mother died. 

Ridge O'Brien: Aaron's second in command. 

Callie: Aaron's close friend and advisor. Is hinted at having a history with Kace, although nothing is ever confirmed.

Sterling: A test kid. Weird, super-smart, and best friends with Maggie. A little off in the head, due to being kept in isolation and experimented on by Making Perfect for a large percentage of his life. 

Maggie: Another test kid. The only person in the world Sterling trusts. Caring, happy, and unwaveringly faithful, she embodies the optimistic side of the Star Formula that is necessary for stamina.