John le Carre's The Constant Gardener

In a remote area of Northern Kenya, activist Tessa Quayle is found brutally murdered. Tessa's companion, a doctor, appears to have fled the scene, and the evidence points to a crime of passion. Members of the British High Commission in Nairobi assume that Tessa's widower, their mild-mannered and unambitious colleague Justin Quayle, will leave the matter to them. They could not be more wrong. Haunted by remorse and jarred by rumors of his late wife's infidelities, Quayle surprises everyone by embarking on a personal odyssey that will take him across three continents. Using his privileged access to diplomatic secrets, he will risk his own life, stopping at nothing to uncover and expose the truth - a conspiracy more far-reaching and deadly than Quayle could ever have imagined.