Aristotle's Poetics emphasizes the importance of plot as the 'soul of tragedy,' insisting that a tragedy must have a coherent structure with a proper beginning, middle, and end. He highlights the significance of unity in time, place, and action, arguing against episodic plots and poetic justice. The most effective tragedies incorporate elements of peripety and anagnorisis to elicit pity and fear, with a focus on probability and necessity in the unfolding events.