The plot of Don't I Know You? seems Law & Order-ready: A 12-year-old boy discovers his dead mother in their NYC apartment; clues are gathered, leads pursued, yet the killer roams free. Karen Shepard's investigation unfolds obliquely jumping forward 16 months, then more than a decade, then flashing back to four years before the murder concentrating on seemingly extraneous characters. Her cunningly crafted jigsaw puzzle is colored by vibrant prose (''The sky was the color of sour milk. The backs of his thighs were sweating'') and capped by a you'll-never-guess conclusion that's not the least bit gimmicky. You might want to read it all over again just to follow Shepard's beautifully subtle tracks.