Every writer must decide how to start a book, a play or a narrative. Many start at the beginning of a story, working their way through a middle, and finally a conclusion, so that the story progresses in linear fashion, seldom looking back to anything that occurred before "the beginning." Another literary technique, which is quite common, is starting in the middle of the story, which often requires some back-tracking to explain actions that occurred before the narrative began. This literary convention is called either in medias res or medias in res, meaning “in the middle of things.”
Starting a story in medias res is a long held tradition in the writing of novels, the composition of oral tales and poetry, and now practiced in the modern novel, screenplay, or play. The earliest examples belong to Homer, who begins both The Iliad and The Odyssey in the middle of things. Readers will note, for instance, that The Iliad begins with the Achaeans already in the middle of the battle with the Trojans, and The Odyssey starts with most of Odysseus’ journey home already finished. The background, especially in the latter, is filled in as Odysseus continues to journey home and recounts some of his strange adventures to people he meets.
The advantage of starting a story in the middle is the ability to immediately introduce action, which may then be explained more fully as a narrative progresses. Such explanations aren’t always present. Sometimes, a narrative explores a very small piece of a larger story that is so familiar that people will already know the back story. Alternately, slice of life tales may literally take a slice of someone’s story, a few days, a few years, and begin there, not really creating a conclusion at the end of the work.
The Odyssey, a Homeric epic, begins after the hero's voyage has mostly been completed.
Some of the most celebrated works of fiction, plays, and screenplays use the convention of in medias res. In addition to Homer’s use of this literary technique, numerous Greek plays, like The Agamemnon, make use of it. Dante’s Inferno, the beginning of The Divine Comedy, is frequently cited as one of the prime examples and begins with the line “Midway upon the journey of our life,” (Nel mezzo del cammin di nostra vita).
Many of Shakespeare’s plays begin in the middle of things. Hamlet takes place after his father has died, for example, and A Midsummer Night’s Dream begins in the middle of several arguments. These beginnings in the middle inspire immediate action with some dialogue devoted to what has transpired prior to the start.
Dante's "Inferno" famously opens in medias res.
Numerous films begin in medias res. The Godfather is a prime example, as is Star Wars: A New Hope, the first film in that franchise. Only later through the chapters following and the chapters previous was the full story completely fleshed out.
Many writers find that it can be a fun exercise to take a well-known tale and change it to begin in the middle or toward the end. Fairytales work very well for this, and the storyteller might try starting Cinderella with her running away from the ball, or Hansel and Gretel with the death of the witch. This practice helps the writer learn how to tell a story from a different angle. Cinderella might inspire her true love with stories of her cruel past, or the awful character of the stepmother be revealed in a series of flashbacks as Hansel and Gretel attempt to make their way home.