Red King, White Knight(1989)

The CIA hears of a KGB scheme to assassinate the Soviet General Secretary and enlists Stoner, an agent retired for 10 years, to go to Russia to investigate. He verifies the plot, but then has trouble leaving the country. In the meantime, the U.S. policy makers struggle over whether or not to inform the Soviets of the plot. Stoner's problems are complicated by the renewal of an affair with Anna, a Russian, as he tries to convince her to defect.