A simple phone call disrupts Nell Williams's well-ordered life. Her mother, Mary, is in a hospital in Vermont. But her mother is supposed to be safely tucked away in an assisted-living facility in Massachusetts, so Nell can't fathom why she would be so far from home.

After notifying her sister, Bridget, Nell hops on a plane and rushes to her mother's side. There, she discovers that her mother has been living a second life. Mary has another home and a set of complex relationships with people her daughters have never met.

When Nell and Bridget delve deeper into their mother's lakeside hideaway, they uncover a vault of family secrets and the gateway to change for all three women.