The search for a daughter. Lady Coulton gave up the baby that would have ruined her marriage, born when Lord Coulton was abroad. Now that her husband is dying, she asks Kate to find Sophia. A haunted library. It is forty years since the ghost of a dead librarian haunted the old library, yet the stories have begun again. Kate does not believe in ghosts but obligingly takes part in a ceremony to expel the restless spirit. Shockingly, there is a body in the basement, strangled, and covered in dusty volumes from a fallen bookcase. It is Dr. Potter, a mathematician. A killer on the loose. Dr Potter's body is taken away. The police find a sick man sheltering in the basement. He is an Italian, Umberto, an organ grinder and owner of a lively Capuchin monkey. Umberto becomes the prime suspect and will be charged with murder. Kate goes with Umberto to the infirmary. But he is too weak to be a suspect. And now Kate must set out to find the real culprit.