Vanished by Joseph Finder

Lauren Heller and her husband Roger, a brilliant executive at a major corporation, are attacked in a Georgetown parking lot after an evening out.†Knocked unconscious by the assailants, when Lauren comes to, her husband has vanished without a trace. When no one else, official or unofficial, will take her seriously and help, Lauren calls the only person left who might: her husbandis estranged brother, Nick Heller, a high-powered investigator with a corporate intelligence firm in Washington, D.C.