Top Secret/SI was the second edition of TSR’s not particularly popular spy RPG. The SI stood for Special Intelligence, a fact I am only just learning today. My sleepless nights are now over. I believe our teenage gaming group played this a grand total of three times, all of which I remember as being fun. It was just that we tended to be fickle in our tastes and we still tended towards the old Games Workshop wargames. We played one game using the standard rules, which was very much in the James Bond / Man From UNCLE mold. You played agents of ORION battling the evil espionage group WEB, it was all very sixties spy movie-like, girls, gadgets and glamourous locations.
Then, the other two games were using the adventure settings books they had brought out for it. “Agent 13” was the first, a setting recreating 1920s and 1930s pulp adventures. I’m not sure if this was based on the novels by Flint Dille (GI Joe/Transformers) and David Marconi (GI Joe/Enemy of the State/Die Hard 4.0~!~!) that TSR printed, or vice versa.
The second was F.R.E.E. Lancers by Jeff Grubb, that was plain nutty. Grubb, who’d been behind TSR’s Marvel RPG, spot-welded super powers and cyberpunk onto the espionage genre, resulting in a gloriously goofy mess. I can’t recall the details, but I do remember it being great fun.