The Betrayers is the tenth novel in the Matt Helm spy series by Donald Hamilton, which originated with Death of a Citizen in 1960. This novel was first published in 1966. It was reissued in 2014 by Titan Books. Up to this point, Hamilton had maintained a publishing schedule of at least one Helm novel annually, sometimes more than one. Readers would have to wait until 1968 until the release of the next Matt Helm novel, The Menacers. Source: Wikipedia (en)