Savaging the Dark by Christopher Conlon

Mona Straw has it all—beautiful daughter, caring husband, lovely home, fulfilling job as a middle-school teacher. But one day a new man enters Mona's life and turns it upside-down, their passionate affair tilting her mind to the edge of madness—and murder.
Her lover's name is Connor. He's got blonde hair, green eyes...and he's eleven years old.
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"One of the 50 Best Horror Novels of All Time" —Paste Magazine
"Top Ten Horror: 2015" —Booklist (starred review)