Escaping an uncertain past, Mary Demore moves to a new school and meets Ainsley Wintertide and her friends. They soon learn about her succubus heritage, her aversion to feeding on humans, and her not getting along with her family. As her condition worsens, they all—especially Ainsley—try to help.
Their research leads them to a domain ruled by a vampire. After testing them, she introduces them to the alchemist who completed the famed, albeit flawed elixir of life. The alchemist agrees to help in return for some ingredients.
After getting the ingredients—and helping Jane O’Young and Gina Evelyn reconcile from a recent incident along the way—they complete the potion and uncover an important truth from Mary’s past. With it, Mary finally accepts her heritage and her family.
The prequel to this story is The Staunch Hawthorn. Its sequel is Writing Her Own Story.
A more detailed outline can be found here: Mary’s Eternal Companion Outline
These are listed in alphabetical order.