The Eiger Sanction. Poster of the 1975 movie and cover of the 1972 book
VS3
The Eiger Sanction
Trevanian, 1972
movie vs book
Clint Eastwood, 1975

Art professor and mountaineer Jonathan Hemlock is a retired government assassin called on to return to work for two more sanctions, a euphemism for officially approved killings. During his career with a secret government agency called C2, Hemlock amassed a private collection of 21 rare masterpiece paintings, paid for from his previous sanctions.