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David Suchet remains unrivaled in his portrayal of Hercule Poirot, the fussy Belgian detective at the heart of Agatha Christie's most famous mysteries.

But in the latest "Masterpiece Mystery" adaptation, "Three Act Tragedy" ( 8 p.m. June 19, PBS/WTTW in Chicago; *** out of four), he meets his acting match in Martin Shaw, who plays Sir Charles Cartwright, Poirot's friend and a famous actor who is ready to retire.

The story begins at Sir Charles' ocean-side home, where he throws a party for, as he tells Poirot, a stage play's worth of interesting characters. The party ends in tragedy when the local vicar suddenly dies after drinking his cocktail. An inquest--and Poirot--rule out foul play, but Sir Charles and his young friend, Miss "Egg" Lytton Gore (Kimberley Nixon) are not satisfied.

Christie fans won't be, either.

A month later, a similar tragedy strikes at another party with an almost identical guest list. Poirot, now having no doubt that a murderer is on the loose, leaves his Monte Carlo vacation with Sir Charles and heads to Yorkshire to investigate.

Sir Charles and Egg are more than eager to help Poirot look into the suspects who include a gambler, a fashion designer, an ambitious new playwright, a penniless aristocrat, Egg's rejected suitor and Sir Charles' faithful servant.

But as always, only Poirot's little gray cells can figure this out, and watching that remains the joy of this series. "Three Act Tragedy" doesn't rival last year's taut adaptation of "Murder on the Orient Express" for suspense, but it's one clever mystery.

As I mentioned, Shaw steals the show, obviously relishing the role of the gregarious stage star and amateur sleuth. But the supporting cast, including Art Malik, Jane Asher, Kate Ashfield and Ronan Vibert (of "The Borgias"), are wonderful as well.

I've probably read all of Christie's books, and like the way screenwriter Nick Dear kept the best of this book. Poirot almost always gathers all the suspects together for the big reveal, but in "Three Act Tragedy" it is especially delicious, and ends with one of Christie's best lines.