Two high school outcasts form a lifelong friendship after the death of a teacher they both despised.

In "The Mary Purse," Perrie Spock is an honor student dubbed "Mortuary Perrie" by the cool kids at Vardo High School because she assists her mother in the family funeral home business. Maria de Gudadalupe Contreras y Villareal, an immigrant student dubbed "Babe the Blue Ox" because of her size, works with her mother to clean in the funeral home. The two girls have little in common until Mrs. Figgart, the AP English teacher, dies in a car crash. While helping her mother undertake the body, Perrie discovers a stolen treasure and returns it to Maria.

Perrie's act of kindness forms a lifelong bond with Maria. Years later, Perrie returns to Vardo to run the family funeral home, and Maria becomes her sidekick and assistant mortician. Together, Perrie and Maria discover more mysteries about the dead in the quaint town of Vardo. As "last responders", they retrieve and care for the dead—while solving mysteries and comforting the living.