Red King, White Knight (1989)

The C.I.A. hears of a K.G.B. scheme to assassinate the Soviet General Secretary and enlists Stoner (Tom Skerritt), an agent retired for ten years, to go to Russia to investigate. He verifies the plot, but then has trouble leaving the country. In the meantime, the U.S. policymakers 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 (Dame Helen Mirren), a Russian, as he tries to convince her to defect.