The Mists of Fear - John Creasey

It seemed to be only a light vapour, but it was evil incarnate, strong enough to knock a tough man down. Dr. Palfrey is up against an enemy greater than any he has faced before, who moves in a white, insidious mist that brings death to all but one. The swirling fog dissipates just as suddenly as it appears and the people engulfed within it simply disappear. They are the sons and daughters of politicians, religious clergy, and other notables. The world is threatened with disaster, but Palfrey is completely puzzled by the terror being ranged .