The Vanishers by Donald Hamilton

People are vanishing without a trace. And the disappearances are getting closer to home—the next likely target is Mac, Matt Helm’s shrewd old boss. To get to the bottom of the mystery, Helm follows two beguiling and treacherous women, who lead him all the way to his ancestral home—Scandinavia. With a coup from within the agency, and a terrorist threat from without, it’s clear that nobody can be trusted.