The first part is an icon-driven strategy game, whereas parts two and three are more traditional adventure games. Part three is different on the C64 than it is on the Spectrum.
An official guidebook, The Fourth Protocol - Playing the Game, written by the game's authors Gordon Paterson and John Lambshead, was published in 1986 by Century Communications Ltd.
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Very unbalanced game consisting of three completely seperate parts. The first one is really good, but hardly Adventure-like (you sit at your desk, assign agents to follow suspects and deal with bureaucracy and planning). The second and third episode are made in Adventure style, but not nearly as good. The third part is even a different one on the C64 and on the Spectrum.
Should Frederick Forsyth be added to the author list? He did write the book, and the storyline of the game does resemble it. It's not identical, IIRC (it's been a while since I read the book or played the game), but it's not a case of "in name only".
Richard, unless Frederick Forsyth had any input in creating the game (see Douglas Adams and The Hitchhiker's Guide to the Galaxy) adding Forsyth's name to the author list would be akin to crediting J. R. R. Tolkien or Jeffrey Archer for the adventures based on their books.