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Upon being diagnosed with terminal cancer, selfless suburban housewife Mary Scott (Margaret Sullavan) makes the ultimate sacrifice: she decides to keep the unpleasant news from her husband, Brad (Wendell Corey), and daughter, Polly, to avoid devastating her loved ones. Instead, Mary encourages Brad's affair with a co-worker (Viveca Lindfors), and even grooms the other woman to take her place. But as Mary's illness progresses, keeping it a secret presents a considerable challenge. Wikipedia