David Suchet returns as Hercule Poirot, Agatha Christie’s endearingly fastidious sleuth, in three bafflingnew casesbased on her classic novels. As seen on the PBS Masterpiece Mystery! series.THREE ACT TRAGEDY:  After guests at successive dinner parties mysteriously drop dead, Poirot teams up with an old friend, retired stage star Sir Charles Cartwright (Martin Shaw), to ferret out the killer. Guest stars include Jane Asher, Art Malik, and Kimberley Nixon.THE CLOCKS:  As Britain readies for war, Poirot journeys to Dover to help the son of an old friend solve a case involving an unidentified corpse and four mysterious timepieces, all stopped at precisely the same time. Anna Massey guest stars.HALLOWE’EN PARTY:  Crime novelist Ariadne Oliver (Zoë Wanamaker) calls Poirot in to investigate the macabre murder of a young girl at a children’s costume party who claimed to have witnessed a killing. Also stars Sophie Thompson, Deborah Findlay, and Amelia Bullmore.