Mary Willis Walker is an American crime fiction author. Walker began writing in her mid-forties, which she characterized as " 'pretty late to start' ". She spent two years writing her first published thriller, Zero at the Bone, which was published in 1991. Her second Texas-based mystery, Red Scream, was Walker's first to feature sleuth Molly Cates. Red Scream won the Best Mystery Edgar Award in 1993. Under the Beetle's Cellar, published in 1995, was Walker's third mystery.