“This affair must all be unraveled from within.” He [Hercule Poirot] tapped his forehead. “These little gray cells. It is ‘up to them’—as you say over here.”

Poirot insists that the mystery will be solved not by force, luck, or purely physical clues, but by disciplined reasoning—“unraveled from within.” His gesture to his forehead foregrounds his trademark faith in intellect and psychology: the mind’s ability to order facts, detect patterns, and infer motive. The line also highlights Poirot’s outsider status in English-speaking settings; his slightly formal phrasing and the aside “as you say over here” underline his Belgian identity while showing his adaptability. More broadly, the quote encapsulates Christie’s classic fair-play detective ethos: the decisive breakthrough comes from interpretation and synthesis—making sense of what is already present—rather than from sensational action.