In I Am Bloody Mary movie, Mare and her fiancé Nick may not have much money, but they have love. As a foster kid with no family of her own, Mare dreams of a wedding with Nick’s family by their side, but Nick is secretive about his estranged relatives. Then, unexpectedly, his mother arrives, warmly inviting Mare into the wealthy and mysterious Thornwood family. She even offers to host the wedding at their grand estate. But the morning of the ceremony, a horrifying discovery shatters Mare's dream, and she realizes she’s not walking into a happy-ever-after, but into a nightmare twisted by the Thornwood family’s dark history--one that might end up killing her.