"In Media Res" is an editing manipulation whereby the story begins partway through / or at some later point and then we tell the story back up to that point.
In Intouchables / Untouchable (2011), the story begins with Philippe and Driss speeding to avoid the police. We then learn how they got there.
In Trainspotting (1996), the story begins with Renton running. We then learn what led to that.
In Media Res is often used to capture the audience at the start in the hope that they will remain engaged enough to follow it back to that point.
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