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. Nick finds himself on a collision course with one of the most powerful and secretive corporations in the world, whose minions will stop at nothing to protect the secrets that Nick Heller is determined to uncoverosecrets that reach into the highest levels of the government†. . . and may get Nick and everyone he's trying to protect killed.