'Kim', by Rudyard Kipling. Nothing over-stated but contains everything: brush contact, humint handling, observation, assasination, enlisting support, espionage.
'Seven Pillars of Wisdom' by T.E. Lawrence, for when the politics are beginning to fail and more direct action is needed. The man was a ruthless, single-minded hero of the old school, but not in the shoot-em-up style. Skip the bit about pretty camels though.