Tick Tock by Dean Koontz (Paperback) 1997 Ballentine Books.
Tommy Phan is a successful detective novelist living the American Dream in southern California. One evening he comes home to find a small rag doll on his doorstep. It’s a simple doll, covered entirely in white cloth, with crossed black stitches for the eyes and mouth, and another pair forming an X over the heart. Curious, he brings it inside.