At Close Quarters (1987)
The British ambassador to the Soviet Union is killed by a Palestinian assassin. A young diplomat called Holt survives and is the only witness who can identify the killer. The British government decide on vengance and send Holt and an Israeli sniper into the Lebanon on a foolhardy mission to find the terrorist training camp in the Beqa'a valley and kill the assassin.
One of my favourites of Seymour's books from the 1980s, and one I would also like to see filimed.
American title: An Eye for an Eye