Sheldon and Davy Vanauken knew at once that they shared the most rare of loves. Basing their lives on a dogma of complete sharing and a unselfish focus on what was best for both, they created what they dubbed the "Shining Barrier" to safeguard their tiny, self-sufficient world of two from everything else. Then an Oxford don named C.S. Lewis came into their lives, bringing with him a Christianity unlike that which they had scorned years before, and they started to wonder if they were as untouchable by the world as they had once thought. When both became Christians, their love continued, stronger than ever. But when Davy became fatally ill, everything they thought they understood was again called into question.

A Severe Mercy is Sheldon's story of the love he and Davy shared and his struggle to cope with her sickness and death. His journey of theological exploration is buttressed throughout by remarkable letters from C.S. Lewis that offer compassion and theological insight, as well as a penetrating glimpse into Lewis' own burgeoning relationship with Joy Davidman, a relationship that would in many ways parallel that of Sheldon and Davy.