The shadow of your smile - Mary Higgins Clark

At age eighty-three and in failing health, Olivia Morrow knows she has little time left. The last of her line, she faces a momentous choice: expose a long-held family secret, or take it with her to her grave.

Olivia has in her possession letters from her deceased cousin Catherine, a nun. These letters reveal that, at the age of seventeen, Catherine gave birth to a son and gave him up for adoption and they identify the father as Alex Gannon, a world-famous doctor and scientist.

Now, two generations later, Catherine’s granddaughter, Monica, stands as the rightful heir to what remains of the Gannon family fortune. But in telling Monica who she really is, Olivia would have to betray Catherine’s wishes and reveal the story behind Monica’s ancestry.

As the pressure of Olivia’s impending choice weighs down on her, little does she realize that Alex Gannon’s grand-nephews—who are currently exploiting the Gannon inheritance to fund their profligate lifestyles—will stop at nothing to silence Olivia and prevent Monica from learning the secret.