New Orleans is overwhelmed by yellow fever in the summer of 1833, and Benjamin January works through the nights at Charity Hospital while continuing to teach music by day. A request to carry a message from a runaway enslaved woman draws him into the affairs of a wealthy household already strained by illness and secrecy.
As storms and epidemic deaths isolate parts of the city, January uncovers a chain of deception involving slavery, inheritance and murder. His medical training helps him distinguish disease from deliberate harm, but pursuing the truth threatens both his freedom and the people who trusted him with the message.