This is the second Agatha Christie adaptation to star Peter Ustinov as the dopey but likable Belgian inspector Hercule Poirot, and it proves--as in DEATH ON THE NILE--that his is the definitive, though not the most faithful, persona. The setting is an idyllic island retreat (filmed in Majorca), where Ustinov is investigating the death of a bitchy stage star, Diana Rigg. The suspects are many--a cheated biographer, Roddy McDowall; a pair of financially dependent Broadway producers, James Mason and Sylvia Miles; the dead woman's husband, Denis Quilley; his lover, Maggie Smith; a millionaire, Colin Blakely; and a husband and wife, Nicholas Clay and Jane Birkin--and no alibi is too strong for Ustinov. Though director Guy Hamilton, who previously directed THE MIRROR CRACK'D, has tried to make the Christie formula more cinematic by trimming the number of characters and streamlining the plot, the picture is still rather uninteresting. Only the performances, the lovely location, and some Cole Porter tunes make it worth watching.