Criminal Minds (2005 TV Series) - Season 18 - Episode 1: "Swimmer's Calculus"

The BAU as they hunt a sadistic pool killer, Franklin Fowler, whose victims are found drowned with distinctive rib cage injuries. Meanwhile, Rossi faces scrutiny over Voit's prison attack, while Voit awakens from a coma, threatening those around him. The team races against time to save two victims trapped in a backyard pool, uncovering chilling connections between Voit and Fowler’s dark network.