Late in her life, acclaimed novelist Elizabeth Delamere makes a request of her therapist, Doctor Newman: she asks him to oversee the publication of her last book after she dies. It is a memoir in which she reveals that she is Evelyn Dick, the notorious "torso murderer" acquitted on appeal of dismembering her husband, and convicted of killing her infant son. In 1958 she was paroled, and disappeared into the mists of history.

In Blue Moon, James King draws on the historical case of Evelyn Dick, and imagines her life after her release from prison. It is a life in which she travels to Vancouver, renames herself, and settles into a position as sales clerk at Duthie Books on Robson. There she meets Ethel Wilson, begins therapy, and tries to understand the events that led to her imprisonment and current life. She also begins to write, and finds herself a successfully published author.

But did she murder her husband? Is she guilty of neglect of her baby boy? Was her life as Hamilton's most notorious prostitute her responsibility? With the help of Doctor Newman, she attempts to come to understand the violence in which she was involved, her sense of guilt, and the essential truth of her innocence.