Read Gamespot/Sid Meier coverage of Covert Action
Microprose's Covert Action attempted to combine spy action and research. It's something I play a lot for a week or so and then stop altogether. I find the breaking and entering rather addictive.
Eventually you unravel the masterplan.
Overall, the gameplay is arcadey and fun. More fun certainly than Accolade's Third Courier - one of the other few spy simulators out there. Unfortunately, neither makes you feel as cool as James Bond can seem.
and Sid Meier's reflections on Covert Action.