Cassiopeia "Cassie" Sullivan
The main protagonist of the novel, Cassie is a sixteen-year-old girl described as short with curly strawberry-blonde hair. She was an average girl before the invasion, introspective and a little disappointed by the quality of her social life. Her mother died in the third wave and her father was executed by Commander Vosch at the refugee camp the Sullivans were staying at. Her younger brother, Sammy, is taken away with the rest of the children to Camp Haven. She is later on shot and rescued by Evan Walker, whom she starts a relationship with and later finds out to be a Silencer. Although suspicious of him, she goes with him to Camp Haven to rescue Sammy and Ben Parish, a boy she had a crush on back in school.
Evan Walker/the Silencer
Evan is a brawny, good-looking boy from rural Ohio whose family was wiped out in the third wave. He is a Silencer and rescues Cassie after shooting her. They become romantically involved. He then goes with Cassie to Camp Haven and disappears inside, but manages to get Cassie, Sammy, and Ben out.
Ben Parish
Ben is a popular football player and honors student in the same high school as Cassie. He contracts the plague in the third wave but is "rescued" and taken to Camp Haven, where he is given the nickname "Zombie." The rest of his family, unfortunately, died. He finds out that the soldiers are actually aliens in disguise and eventually escapes with Cassie and Sammy. Ben becomes like an older brother to Sammy.
Mitchell
Mitchell is a boy to whom Cassie lent a highlighter on the third day of the waves. He and Cassie go on a Starbucks date in her backyard and discuss the invasion.
Dad
Cassie's father is a sweet, gentle man who hovers in the background when Cassie is on dates and shows her the stars. He enjoys movies like Close Encounters, E.T., and Star Trek. He dies when the soldiers who come to "rescue" them load up the children on school buses and then kill the adults. He helps Cassie escape this fate by sending her to fetch Crisco back.
Sammy Sullivan/Nugget
Cassie's younger brother was taken away to Camp Haven, where he goes by the name Nugget. He gave Cassie his teddy bear so she wouldn't be scared and she is determined to find him again. He eventually escapes with Ben and Cassie.
Mom
Cassie's mother died in the third wave of the plague. She enjoys watching TLC while cooking.
Lizbeth
Lizbeth is Cassie's good friend whom she texts about Mitchell and Ben; she is presumed dead.
Crisco
A greasy-haired grave robber who tries to have sex with Cassie, he is killed when Cassie is sent back out to get him by an Other posing as a human soldier.
Lieutenant Colonel/Commander Alexander Vosch
The sadistic, cruel leader and mastermind of the alien soldiers. He is originally thought to be a hero at Camp Haven but reveals his true self by killing Cassie's father.
Dr. Pam
She is the doctor at the facility where Sammy is admitted, called Camp Haven. She microchips and maps all of the children. Cassie kills her while saving Sammy.
Corporal Parker
He is a medic who befriends and comforts Sammy on the bus ride to Camp Haven. He labels Sammy red and Megan green, sending her to a different part of the Camp. He appears again when Cassie is infiltrating the army base Wright-Patterson.
Reznick
A harsh drill instructor who works at the Camp and drills Ben and Sammy, he is later revealed to be an Other who will kill the squad if they don't fulfill their mission. Ben and Ringer remove their implants and kill him.
Members of Squad 53
Squad 53 consists of the following characters:
- Ben, 17, is called Zombie.
- Sammy, 5, is called Nugget.
- Tank goes Dorothy (i.e., crazy) and is sent to the psych ward where he overdoses.
- Flintstone, 16, acted as the leader before being replaced by Ben.
- Dumbo, 12, has big ears and a quick smile, and acts as the squad's medic.
- Poundcake, 8, never talks but is the best shooter.
- Oompa, 8 or 9, is a chubby kid who is the worst at everything but eats the most. He dies on their first mission. His real name is Kenny.
- Ringer is sent to replace Tank after he dies. Her real name is Marika. She and Ben flirt with one another.
- Teacup, 7, worships Reznick and Ringer. She is distraught by Oompa's death.
Sissy Parish
She is Ben's younger sister who is killed when robbers attack her home.
Crucifix Soldier
He is an unknown, wounded soldier who Cassie kills in the grocery store when she sees a flash of metal in his hand, later revealed to be a metal crucifix.
