Opening in the middle of the action, then filling in how the characters got there.
In medias res (Latin, 'into the middle of things') starts the story already in motion - a chase, a confrontation, a disaster underway - rather than with setup. It hooks the reader with momentum first and supplies the context afterward, once they have a reason to want it.
The technique trades orientation for propulsion, so the writer owes a quick anchor: enough grounding that the opening chaos means something. Overdone, it's a cold open with no follow-through; the promise of the fast start is that the backstory, when it comes, will pay the excitement back.
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