Meg Murry
The older sister of Charles Wallace and co-protagonist with him. Her character was first seen in the prequel to this novel and the first in the Time Quartet, A Wrinkle in Time. She often misbehaves, but is good at heart. Through A Wrinkle in Time and A Wind in the Door, she is shown to struggle with self-esteem and self-image issues, as well as feeling unpopular or even ostracized.
Her character deals with feelings of resent toward her old principal, Mr. Jenkins, who refuses to help her improve Charles' school life. This opens old wounds, and throughout the narrative, she is challenged to maintain empathy toward Mr. Jenkins instead of becoming overwhelmed by her feelings of resent toward him.
Charles Wallace Murry
Charles Wallace, the younger brother of Meg, is a smaller-than-average boy with blue eyes and a genius-level intelligence that often leaves him dealing with feelings of isolation and unpopularity, much like his old sister did when she was his age. In addition to this, he also falls ill to a strange, cosmic disease that robs him of his breath.
When the disease is seen to be the direct attack of a cosmic 'enemy,' called Echthroi, the main characters have to travel inside Charles' cells' mitochondria to convince his farandolae to mature correctly and function well, despite the enemies' attacking.
Mr. Jenkins
Mr. Jenkins is another returning character from A Wrinkle in Time, and his conflict with Meg Murry is an important relationship in the plot of this novel as well, specifically, Meg's perception of Mr. Jenkins after what she perceives to be his antagonism of her and her family. Mr. Jenkins is an important lesson in the narrative for Meg to continue viewing others empathetically, even when they are a disappointment and frustration. In the novel, he refuses to help Meg, but in the end, he also benefits from the cosmic salvation of Proginoskes.
Calvin O'Keefe
Calvin returns from A Wrinkle in Time, but this time in a more minor role. He assists Meg and Charles Wallace in discovering the secret behind the 'drive of dragons.' His character doesn't deal with the popularity and image issues that the Murry siblings face, but instead he struggles with the challenges that poverty forces upon his family.
Proginoskes
This cherub, whom Meg affectionately refers to as Progo, is an extraterrestrial alien who resembles an apocalyptic angel, having many wings and eyes like the seraphim in the Biblical book, the Revelation of John. His name means 'foresight' or 'foreknowledge' in Koine Greek, and his character is described as one who names, specifically, he is a namer of the stars. He teaches the protagonists how to use telepathy, and assists them in their quest, eventually sacrificing himself for their salvation, a notably messianic act.
