Mount Mercy Hospital for the Criminally Insane is an insane asylum on Little Governor's Island, New York. Aloysius Pendergast's Great-Aunt Cornelia was confined there after she was convicted of murdering her family.

After Cornelia's death, Pendergast arranges for Constance Greene, who has been committed for the apparent murder of her infant son, to be given her old room at Mount Mercy.

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