The Nature of Secrets by Debra Webb

Legal investigator Finley O’Sullivan has had a difficult year in the wake of her husband’s murder. But in her line of work, there’s no time to grieve. Her job is to protect the firm’s clients and defend their innocence through grueling investigative work.
Ellen Winthrop is a force to be reckoned with in the financial world. In a male-dominated industry, she shattered the glass ceiling by empowering and promoting women. But now her husband is dead, killed in the Winthrop family home—and she stands accused of his murder.
Finley, as the investigator at the firm Ellen Winthrop hired to defend her, has a clear objective: prove that Ellen didn’t do it. But the deeper Finley digs into the Winthrops’ marriage, the more she starts to doubt Ellen’s story. The uncomfortable truth is that Ellen Winthrop may in fact have killed her husband.

And he might not have been the first.