All Our Tomorrows by Catherine Bybee

When Chase Stone’s estranged father dies, leaving his multibillion-dollar business to his children, no one is more surprised than Chase. Growing up outside of the high-stakes world filled with human vultures, Chase and his sister, Alex, are less than enthusiastic about stepping into their father’s shoes. That is until they learn of a half brother they didn’t know existed and must find to share their inheritance with.
Piper Maddox was the elder Mr. Stone’s übercapable assistant—abruptly fired two weeks before his death. She knows everything about Stone Enterprises and the man who built it. But Piper has no desire to work for another member of the Stone family. Even one as down-to-earth as Chase.
Desperately needing financial security, Piper agrees to return so long as kissing up to Chase and accepting unwanted advances are not part of her job description. A promise that becomes a serious hurdle for both of them. Piper and Chase scramble to find the third Stone sibling before the media does, sharing secrets along the way. Secrets that can bring them together or tear them irrevocably apart.