The Eiger Sanction, by TrevanianRead about the other entries on the list.
Dr. Jonathan Hemlock is an art collector and mountaineer with a secret side-job as an assassin who takes contracts targeting other assassins who have killed American agents. To kill his latest target, he must join a group of mountain climbers tackling one of the most dangerous climbs in the world, figure out which one of the men is the subject of the sanction—and survive.
--Marshal Zeringue