Where or When - Anita Shreve

What would you do if out of the blue, you received a letter from your first love? Sin Richards sees no reason why she can't write back to Charles Callahan. After all, it's been thirty years and they are both married with families. But when they decide to meet again, an innocent correspondence becomes a dangerous intimacy. Swept up in the past and consumed by an obsessive love, Charles and Sin risk everything to be together. A heart-wrenching, suspenseful story with an unforgettable conclusion, Where or When is also a 'thoughtful, beautifully written contemporary romance' (The Washington Post).