Lagrasse follows the story of Matty McKenzie, a young Scottish woman who inherits a mysterious old house in a medieval town in France from her late, estranged uncle. She travels out to the house with her dog after a break-up with her long-term boyfriend who she could never quite make it work with. She intends for it to be a brief trip, but, when she arrives, she finds herself caught up with a series of strange events and the house's dark history - not to mention the beautiful local librarian, Emma.
Matty, who has spent her life dating men, starts to fall for the new woman in her life, and tries to uncover the truth behind her uncle, his house, and everything that has brought her to France.