Emma Carter had grown used to feeling the walls close in around her—boardroom politics, Jack’s hot-and-cold affection, and the ever-present scrutiny of the media. But nothing could have prepared her for the bombshell delivered that crisp morning in the study of the Carter estate.

She had just finished a video call with her startup’s advisory board when she found a sealed envelope waiting on the desk. The envelope was addressed to her in her father’s handwriting—familiar, precise, and ...