Kevin Costner is Lieutenant Commander Tom Farrall, a rising officer in the US Navy. He returns home after a mission to see his on-again-off-again girlfriend (Sean Young before the Catwoman debacle) and discovers that she's been "entertaining" the Secretary of Defense (played by Gene Hackman). Naturally Farrall isn't too happy with the arrangement, but since he loves his girlfriend he puts up with her infidelities.
When Sean Young turns up dead, Farrall is all but certain the Secretary is behind it. An investigation begins into Sean Young's death and it quickly balloons into an elaborate charade of misdirection and cold war boogeymen. Farrall is ordered to head the investigation but it's soon obvious that all the evidence points to him because of his secret relationship with Sean Young. The steady pace picks up during the final hour and a half and culminates in a dramatic flourish that is equally surprising and satisfying.
I've said in the past that any movie with Gene Hackman is going to be pretty good and No Way Out is in no way an exception. You could also say that nobody plays Kevin Costner better than Kevin Costner and in this movie that actually works ok. Will Patton (The Postman) is Gene Hackman's assistant and his performance is a testament to his unparalleled ability to play deranged men of authority.