Love Beyond Reason - Sandra Brown

In this rapturous romance, a woman grieving her sister's death vows to protect herself and her newborn niece — even if it means turning away the dashing and irresistible heir to a Texas oil dynasty.
Katherine Adams will never marry a Manning — not if she can help it. Her sister Mary's fairy-tale marriage into the family's wealthy, powerful dynasty turned into a nightmare of abuse. And on the night her playboy husband was killed in a car accident, Mary died in childbirth. Now, the savvy, smart, and very angry Katherine has vowed to protect her sister's child, even if it means rejecting the dashing, charismatic oil man who shows up at her door.
Katherine wants to believe that Jason Manning isn't like his ruthless family. But secrets and lies are part of his heritage. And Katherine could be destroyed by a truth she's afraid to face . . . and a man she can't resist.