Rogue Male by Geoffrey Household is a classic thriller novel, published in 1939.
The protagonist, an unnamed British sportsman, sets out in the spring of 1938 to see if he can get an unnamed European dictator in the sights of his rifle. Supposedly interested only in the stalk for its own sake, he convinces himself that he does not intend to pull the trigger. Caught while taking aim by the dictator's secret service guards, he is tortured, thrown over a cliff and left for dead.
But he comes to and manages to make his way to a port, where he succeeds in stowing away on a British ship bound for London. Once there, he discovers that agents of the unnamed country are aware he has escaped and are after him.