Mary An Awakening of Terror by Nat Cassidy

Nat Cassidy's highly commercial, debut horror novel Mary: An Awakening of Terror, blends Midsommar with elements of American Psycho and a pinch of I'll Be Gone in the Dark.
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Mary is a quiet, middle-aged woman doing her best to blend into the background. Unremarkable. Invisible. Unknown even to herself.
But lately, things have been changing inside Mary. Along with the hot flashes and body aches, she can't look in a mirror without passing out, and the voices in her head have been urging her to do unspeakable things.
Fired from her job in New York, she moves back to her hometown, hoping to reconnect with her past and inner self. Instead, visions of terrifying, mutilated specters overwhelm her with increasing regularity and she begins auto-writing strange thoughts and phrases. Mary discovers that these experiences are echoes of an infamous serial killer.
Then the killings begin...