Therefore, its known narrative elements are not a part of the Doctor Who universe as we, on this Wiki, choose to define it. It may have been the basis for a similar story in another medium, however — and that story may indeed be valid.
Project Zeta Sigma was an unproduced serial that would have been the first story of the Fifth Doctor. It would not have carried on straight from Logopolis and would have featured nuclear disarmament, an alien cold-war scenario with The Master orchestrating it. John Flanagan and Andrew McCulloch co-wrote the serial, which was stopped in 1981 by Antony Root as new script editor with the approval of Barry Letts in the absence of John Nathan-Turner.