Dr. Toby Harper works the night shift in an emergency room. More comfortable with the steady horror and tedium of emergency care than with a normal lifestyle, Toby alienates herself socially from her peers and from her sister. She spends her daytime hours alone with her mother who suffers from Alzheimer's disease. When elderly Alzheimer's patients from the same retirement home start dying mysteriously, Toby is the only one suspicious enough to investigate. As a result she finds herself, her mother, and her own sanity at risk.