In medias res means in the middle of the action.
In medias res is a literary term that is used to refer to a text that starts in the middle of the plot instead of starting with the beginning of the story. When writers employ in medias res, they usually present the events that happened before by means of flashbacks or dialogue. Famous literary works such as Homer's Iliad and Odyssey and Shakespeare's Hamlet begin in medias res; in other words, they go straight to the heart of the plot.