The Resident Patient by Arthur Conan Doyle

A doctor sets up his own practice thanks to a wealthy benefactor who becomes increasingly paranoid and reclusive. When the benefactor is found dead, Holmes discovers a connection to a criminal past and a case of revenge gone wrong. The plot hinges on hidden identities and long-held secrets. Holmes methodically reveals how the patient’s past has come back to destroy him. It’s a tale of guilt, trust, and justice catching up.