Cold, Cold Heart by Karin Slaughter is a short story that first appeared in a collection of stories edited by Lee Child called First Thrills.
That collection was released on June 22, 2010. Cold, Cold Heart was subsequently released as a standalone short story on August 23, 2016.
Cold, Cold Heart Book Description
First comes love.
Then comes marriage.
Then comes revenge.
Fifty-two-year-old Pam has done her utmost as a loyal wife to her now ex-husband John.
He dropped her cruelly . . . but with a terminal illness about to claim his life, Pam now sees an opportunity to settle the score, in a way that no one—not their children, not her ex, and certainly not the reader—will see coming . . .