Death of a Citizen

Blurb

Death of a Citizen is a 1960 spy novel by Donald Hamilton, and was the first in a long-running series of books featuring the adventures of assassin Matt Helm. The title refers to the metaphorical death of peaceful citizen and family man Matt Helm and the rebirth of the deadly and relentless assassin of World War II.
The book sees Matthew Helm, a one-time assassin and special agent for the American government during the war, being reactivated when a former colleague turns rogue and eventually kidnaps Helm's daughter. Afterwards, he agrees to return to duty as an assassin and counter-agent working for a secret agency run by "Mac," his superior officer from 13 years earlier.
Death of a Citizen is notable for its grimness of tone and events as compared to the usual thriller of the late 1950s and early 1960s. After a few initial missteps as his "citizen" persona is shucked off, Helm re-becomes the competent, hard-boiled, and ruthless agent he had been earlier. The ending of the book is particularly shocking, perhaps, in that he shoots down an adversary who is not directly threatening him and then tortures and kills the person responsible for kidnapping his baby daughter.