The Book of Mercy is the story of Edmund Mueller, a retired fireman tormented by memories of his flamboyant wife, Fanny, and her disappearance from his life years ago. His son, Paul, is a missionary in Africa. His daughter, Anne, is consumed by the demands of her medical education.

In his isolation, Edmund becomes fascinated with the art of alchemy, with the works of Paracelsus and Hermes Trismegistus, and the search for the Elixir of Life, which will enable him, he believes, to transmute base metals into gold. The cause of his obsession is a harrowing mystery plumbed by Anne and the resident tending him during his institutionalization.

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Interwoven with Edmund's tale is that of his daughter. Abandoned by her mother while still a baby, Anne learns to take shreds of love where she can find them, from her burdened brother and distant father, then from the string of lovers she pursues. She counts on her wits and willfulness to lead her through her unexamined life.

It is only when she takes up psychiatry and tries to find the heart to deal with her troubled patients that she begins to know herself and comes to understand that her life, like her father's, has been a search for magic - a quest for the transforming power of love.