The patient in room 18

The first Eberhart book featuring Nurse Sarah Keate and Detective Lance O'Leary. A patient, a doctor, and a night watchman have been murdered in room 18 of a hospital catering to the wealthier class of patients. There's a twist ending, but far too much of the "had I only known" and one of the suspects, a mixed-race woman, is treated with the disdain current of the time period (1929) that is grating to modern readers.