Serum follows the life and work of Dr. Gary Davis, a Black physician from Tulsa, Oklahoma, who was working on a treatment for AIDS in the 1990s. This is episode 3: Red Flags and Green Lights.

Reporter Grant Hill gets in touch with one of the last people to have seen Dr. Davis’ serum in action, a Tulsa photographer named Doug Henderson. The conversation reveals that in 2004, Dr. Davis conducted human trials in Africa — enlisting the help of the photographer and celebrity Bishop Carton Pearson to document and publicize his work. What they witness is both astonishing and shocking: Trials with the doctor’s serum seem to leave participants completely recovered. But soon, things fall apart. Dr. Davis appears panicked and afraid for his life. He disappears. Rumors abound. Back in Oklahoma, the photographer is asked to erase all evidence that any of this ever happened. Then he gets word: The doctor is dead.

Serum, a limited-run podcast, is available wherever you listen to podcasts.