In literature, a parallel episode is a scene or chapter in which things that happened to a character earlier happen again in a different context or to a different character. An example is a character attending a baby shower before losing her own baby, then attending a second baby shower afterward. Parallel episodes are used to draw various types of contrasts.
Often parallel episodes are used to demonstrate a change to a character. For example, in Daniel Keyes's classic novel "Flowers for Algernon," Charlie experiences multiple events first as a mentally handicapped man, then as a genius. Keyes uses these parallel events to demonstrate Charlie's differing attitudes and points of view, exposing much of the cruelty that had previously been directed at him.
In "The Lord of the Rings" trilogy, J. R. R. Tolkien frequently used this technique. One notable example is the chapter "The Scouring of the Shire," in which he highlighted the changes to the Shire from a bucolic paradise to a land of corruption and pollution due to the machinations of the evil wizard Saruman.
Parallel episodes often reflect the heart of a story's theme. They also frequently involve similar events happening simultaneously to two different characters as a method of underscoring the differences between them.