On a blustery April day, the quiet, rather private wife of a doctor discovers that her husband has been having an affair. Moments later, driving along a winding country road and distracted perhaps by her own thoughts, perhaps blinded by sunlight, she fails to see Ruth Mitchell up ahead, riding her bicycle. She hits her, killing her instantly. And drives away.

The hit-and-run driver is never found. But the doctor’s wife, horrified by what she has done, begins to unravel. Soon she turns her attention to Ruth’s bereaved husband, a man staggering sleeplessly through each night, as unhinged by grief as the killer is by guilt.

Arthur Mitchell does not realize at first that someone has begun watching him through his windows, worrying over his disheveled appearance, his increasingly chaotic home. And when at last she steps through his doorway, secretly at first, then more boldly, he is ready to believe that, for reasons beyond his understanding, his wife has somehow been returned to him….