Host Ira Glass introduces four characters: Kay McDonald, who raised a daughter named Sue, and Mary Miller, who raised a daughter named Marti. In 1994, Mary Miller wrote letters to Sue and Marti, confessing the secret she'd kept for 43 years: The daughters had been switched at birth and raised by the wrong families. This week's entire show is devoted to the story of Mary Miller's secret and what happened when both families finally learned the truth. (6 1/2 minutes)