Caroline Wallis was living under an assumed name. She just didn’t know it. Growing up in San Marino, California, she went to church at Christmas—her family was Catholic, she believed. There was nothing particularly out of the ordinary about her grandparents, who lived quietly in upstate New York and snowbirded down to Florida in the winters.

Her grandfather, Ben Wallis, died in 2015. A recent graduate of U.C. Berkeley, Caroline joined her family a few months later to help clear out Ben’s Rhinebeck farmhouse, where he and his wife had lived for more than 50 years. They began to uncover unnerving items: passports and immigration papers with unfamiliar names on them; a Hadassah membership card that seemed to belong to a stranger.