The Fever Code characters

Also known as Stephen

Appears from the start

A boy taken into a research compound in the far north after the solar flares and the disease that followed. He was born Stephen and renamed Thomas by the people who took him; he is one of a small number of children the illness cannot infect, which is the only reason he is alive and locked up. Curious, argumentative and desperately lonely, he spends his first years in a single room with a caretaker, a window, and lessons he is not permitted to question.

Appears from the start

The staff member assigned to Thomas when he first arrives: the man who brings his meals, runs his lessons and administers his tests, and who declines to answer anything that actually matters.

Also known as Deedee

First appears in chapter 6

A girl of Thomas's age held elsewhere in the same compound, born Deedee and renamed by the organization that took her. She reaches Thomas first as a voice inside his own head, the two of them being the subjects of an implant that lets them speak mind to mind, and for years she is the only friend he has. She is quicker than Thomas to accept the rules of the place and better than he is at working out what the adults want to hear.

First appears in chapter 8

A senior official in the organization running the compound, composed and unfailingly reasonable, who speaks to the children as though they were colleagues rather than subjects. She regards the program as justified by the cure it is chasing and says so without apology.

First appears in chapter 12

One of the immune children in the compound, and one of the first Thomas meets once he is allowed contact with the rest of the group. Even-tempered and easy to like, he holds the others together where louder boys divide them.

First appears in chapter 12

An immune boy in the same group, blunt, physically confident and openly contemptuous of the tests the children are put through. He treats defiance as a sport, which makes him popular with the others and a standing problem for the staff.

First appears in chapter 15

The chancellor of the organization during Thomas's childhood, and the man whose authority sets the pace and the limits of the program.

First appears in chapter 17

One of the older boys among the immune subjects, serious and self-contained, who takes responsibility for the younger ones without being asked to. The staff notice that about him too.

First appears in chapter 22

A boy in Thomas's group, wary and quick to take offense, who never quite trusts Thomas or the access to the adults that Thomas is given.

First appears in chapter 26

A much younger boy living inside the compound, talkative and starved of company, who attaches himself to Thomas. He is far too young for what the older children are being prepared for, and Thomas treats keeping him out of it as a personal obligation.

First appears in chapter 34

A boy from the second group of subjects the organization runs in parallel, and that group's equivalent of Thomas, carrying the same implant.

First appears in chapter 34

A girl from the second group, paired with Aris in the way Thomas is paired with Teresa.

Also known as Lizzy, Elizabeth

First appears in chapter 34

A girl in the second group of subjects, kept apart from the boys for most of Thomas's childhood. She was born Elizabeth and is Newt's younger sister; the organization separated the two of them, renamed her, and did not intend either of them to find out.

First appears in chapter 36

One of the leaders among the girls in the second group, level-headed and used to speaking for the others.