Lina is a 12-year-old former messenger from the underground City of Ember. She lives with Dr. Hester in Sparks but struggles with the boredom of household chores compared to her active former life. Imaginative and idealistic, she dreams of a beautiful, unruined city and seeks a greater purpose for herself and her fellow refugees.

Doon is a 12-year-old boy who formerly worked in the pipeworks of Ember. He resides in the Pioneer Hotel with his father and is eager to understand the mechanics and science of the surface world. Serious, analytical, and prone to a fiery temper in the face of injustice, he works hard to find his place among the new community.

Torren is a 10-year-old Sparks resident who lives with his aunt. Small and narrow-faced, he resents sharing his limited space, food, and attention with the newly arrived refugees. He idolizes his older brother and frequently acts out out of loneliness and frustration.

Tick is a handsome, sharp-featured older youth from Ember. He channels the refugees' discontent, organizing work projects and vocalizing their frustrations about food rations and poor treatment. He uses his natural charisma to gather followers among the Emberites.

Caspar is a roamer and Torren's older brother. He searches the ruins of the pre-Disaster world for items to bring back to Sparks, though he prefers finding novelties and extinct artifacts over practical supplies. He boasts about his travels and focuses heavily on his own ambitions, often ignoring his younger brother.

Maddy is a stoic young woman who left a failing settlement to become a roamer. Unlike Caspar, she thinks practically about survival and understands the destructive nature of treating others like enemies. She provides a grounding influence during travels in the Empty Lands.

Dr. Hester is the overworked and under-resourced sole medical provider for Sparks. She takes in Lina, Poppy, and Mrs. Murdo as houseguests. Exhausted by her constant duties, she has little time or energy left for her nephew Torren.

Mary is one of the three town leaders of Sparks. Pragmatic and ethically minded, she attempts to guide the village in a way that avoids the corruption and violence of the pre-Disaster world.

Ben is one of the town leaders of Sparks and Torren's uncle. He takes a harsh, protective stance regarding the town's limited resources. He advocates for strict rules and separation between the native residents and the newcomers.

Wilmer serves alongside Mary and Ben as a leader of Sparks. He primarily focuses on wanting the tense situation between the two populations to improve, seeking practical solutions to the resource strain.

Mrs. Murdo is a former Ember resident who acts as the guardian for Lina and Poppy. She provides stability and practical care for the girls as they adapt to the confusing, sunlit world of Sparks.

Poppy is Lina's infant sister. Sickly upon arrival at Sparks, her health slowly improves under Dr. Hester's roof. Her illness demonstrates the physical toll the journey has taken on the refugees.

Edward is the elderly former librarian of Ember. Deemed too old for the manual labor assigned to the other refugees, he feels useless until Doon introduces him to a chaotic stash of books in Sparks' storehouse.

Kenny is a young boy from Sparks whose family hosts a group of Emberites for lunch. He takes a liking to Doon and shows him the town's hidden collection of books in the storehouse.

Doon's father is a former resident of Ember trying to adapt to life on the surface. He provides a sounding board for Doon's frustrations and helps his son think critically about the consequences of physical retaliation.