The Betrayers
Far out in the Pacific, among the sunny islands of Hawaii, a dark venomous plot was being engineered by one of our own agents, an angel-faced man called the Monk, who had a special fondness for high explosives. His target was an American troopship with 3,000 U.S. soldiers scheduled to blow sky high--unless Matt Helm could stop him. But first Helm had to trust the beautiful stranger who claimed to be his sister-in-law, and insisted that his former "wife" had just willed him half a million dollars. [cover blurb]
Donald Hamilton
Donald Hamilton was a U.S. writer of novels, short stories, and non-fiction about the outdoors. His novels consist mostly of paperback originals, principally spy fiction but also crime fiction and Westerns such as The Big Country. He is best known for his long-running Matt Helm series (1960-1993), which chronicles the adventures of an undercover counter-agent/assassin working for a secret American government agency.
Hamilton began his writing career in 1946, fiction magazines like Collier's Weekly and The Saturday Evening Post. His first novel Date With Darkness was published in 1947; over the next forty-six years he published a total of thirty-eight novels. Most of his early novels whether suspense, spy, and western published between 1954 and 1960, were typical paperback originals of the era: fast-moving tales in paperbacks with lurid covers. Several classic western movies, The Big Country and The Violent Men, were adapted from two of his western novels.
Matt Helm
Matt Helm consists of twenty-seven books. The current recommended reading order for the series is provided below.

