A Wind in the Door is the second installment in the Time Quartet by Madeleine L'Engle, following the story of the same protagonists from the first novel, A Wrinkle in Time. This novel continues the story of Meg Murry and her younger brother Charles Wallace Murry, along with Meg's friend and Calvin O'Keefe, all three characters returning from A Wrinkle in Time.
The novel contains both a literal social narrative of the school life of the three protagonists, especially Meg Murry, who continues to deal with feelings of resent against her former antagonist, Mr. Jenkins, who continues to be a source of frustration in her life, and also her brother Charles Wallace, whose genius-level intelligence and insight leaves him isolated by his peer group. The novel also addresses more cosmic concerns, especially through the use of science fiction elements like alien beings named after Biblical angels, and a disease that seems to be both biological and spiritual in nature.
Meg, concerned about her brother's social status in school, reaches out to Mr. Jenkins, who she had hoped would assist somehow with Charles' difficulties, but she is again disappointed by Mr. Jenkins. To her, this seems to be related to Mr. Jenkins' dislike of her and her family. To make matters worse, she then learns that Charles is afflicted by some strange disease that makes it difficult to breathe. Their mother suggests that the illness is actually a microbiological issue with the farandolae in Charles' mitochondria.
Afterwards, Charles Wallace tells Meg about dragons he has seen behind their house. After discovering strange feathers where he claims to have seen the dragons, Meg encounters a monster which resembles her ex-principal, Mr. Jenkins. After the episode, the two are joined by Meg's friend Calvin O'Keefe who helps them learn more about the mysterious 'drive of dragons' that Charles Wallace has seen.
These creatures turn out to be aliens called cherubim (named after an angel described in the Bible), specifically one named Proginoskes (perhaps another reference to the Bible, from Koine Greek for 'foresight'). After this, they encounter a being called Blajeny who charges the three to help fight the Echthroi (Greek for 'enemies').
The first challenge depends on Meg using empathy to distinguish the real Mr. Jenkins from fake replicas that play into her resentment for the man. Afterwards, they are able to identify the cellular disease that is causing Charles Wallace's breathing difficulties. The Echtroi have been afflicting Charles Wallace's farandolae, and to undo the attack, the three travel into his mitochondria where they meet a young farandola named Sporos who they urge to develop properly. This episode proves nearly fatal for the characters, but in the end they are saved by Proginoskes, and Charles Wallace's mitochondrial illness is cured.
