The premise of "Mrs. Dexter" is revealed immediately; we witness the inventive technique used to kill her—a gassing—and there’s a certain originality in how her husband, “Paul” (Peter van Eyck), carries out this action. Afterward, when the police discover the sealed room, they naturally conclude she died by suicide. However, his stepdaughter "Candy" (Mandy Miller) has serious doubts. She insists that she once saw him murder her biological father during a boating trip, and now she’s resolved to uncover the truth. What follows isn't particularly strong, nor is the acting especially impressive—though the final fifteen minutes offer a satisfying feeling of well-deserved punishment that I felt helped redeem the rest of it. The film does run on for too long and feels overly verbose, but if you remain patient, the ending provides something to consider about alternative approaches.

Source on TMDB