Robert Ludlum's The Janson Equation by Robert Ludlum
US Senator James Wyckoff hires former government agents turned private security consultants Janson and Kincaid to locate his teenage son Gregory. Gregory's girlfriend Lynell, a translator, has been found dead in a Seoul hotel, and Gregory has fled the city. But Senator Wyckoff insists his son is innocent, suggesting that Lynell may have been killed because of something she overheard at a recent international conference.
And when Janson and Kincaid realise they're being hunted by an assassin, they suspect that the crime, and the cover-up, were orchestrated by a shadowy unit of the US State Department as part of a larger plot to provoke violence between North and South Korea.