Curtain: Poirot's Last Case (S13E05)

A frail Hercule Poirot revisits Styles with his longtime friend Hastings, nearly thirty years after they first cracked a case together. Their reunion is prompted by the urgent need to thwart a clever and ruthless serial killer who threatens to take more lives. As Poirot confronts his own limitations, he is determined to use his brilliant mind one last time to bring the villain to justice before it's too late.