Sunday (July 27) David Suchet returns as Belgian detective Hercule Poirot. “Masterpiece Mystery” kicks off Season 12 of “Poirot” with two new cases based on the novels by Agatha Christie, “The Big Four” and “Dead Man’s Folly” (Aug. 3).

Watch the above preview of “The Big Four,” which sees the world on the brink of World War II when a murder at an international peace reception reunites Poirot with some old friends. Then next week in “Dead Man’s Folly,” a famous mystery writer creates a murder mystery weekend, but must call in Poirot when it takes a grisly turn.

“Poirot” Season 12 premieres Sunday, July 27 at 9 p.m. ET/PT on PBS.