The Eiger Sanction by Trevanian

In this gripping thriller, a retired art professor and skilled assassin is drawn back into the world of espionage when he is tasked with a dangerous mission to eliminate a target during a treacherous climb of the Eiger mountain in the Swiss Alps. As he navigates the perilous ascent, he must also unravel a web of deceit and betrayal, where allies and enemies are indistinguishable, and survival hinges on his ability to outwit those who would see him fail. The story masterfully blends high-stakes adventure with intricate plot twists, keeping readers on the edge of their seats.

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