< SUNDAY THE END

Here's the backstory, most of which was gradually figured out by the players (apart from exactly what the ludicrously overcomplicated Mysteron plan actually was, but that doesn't really matter.)

The Mysterons had issued their usual threat to Spectrum that they would destroy planet Earth – this time at the climax of a traditional biennial event and that they would use several items of great power to do so. Note: the following section includes the four final answers to the Orange puzzles so it has been blanked out.
[They planned to use the TOX UTHAT (ST:TNG) to render Earth uninhabitable, but they would use a TRILUMINARY (B5) powered by a ZERO POINT MODULE (SG-1) to travel back in time to before man appeared, thus ensuring that they would never evolve. Finally, they would use the Resurrection Glove - nicknamed the RISEN MITTEN (TW) - to keep their Agent alive long enough in the past to carry out his mission.]

Unfortunately, although the Mysterons had tracked down the items to Redemption, their Agent on site (Agent B, of course) was unable to locate them. So he had the bright idea of planting a bomb to destroy the convention and then using the presence of several undercover agents to do his work for him. The plan was that by defusing the bomb and finding the items, they would then obligingly hand them over to The Agency in the form of Agent B. And, failing that, they would at least give them to their contacts (who would have been replaced with Mysterons during the course of the weekend, thus producing the same results.)

Spectrum finally discovered what the plan was, but could only send a coded warning message to the agents in the hotel as there wasn't time to get there in person. Meanwhile the news report suggested that most of the contacts the Agents had met during the weekend had been the victims of some narrow escapes (when, of course, they hadn't in fact survived but had been replaced by Mysterons instead...)

The agents needed to figure out the puzzles which Agent B had set and defuse the bomb. The Orange puzzles gave them the names of the four items (listed above.) The Yellow puzzle told them their password. The Green puzzle gave them the method of finding the code for the bomb.

Answers to those puzzles are here:
[The Yellow puzzle told them to use the passphrase from the original coded message in PR3 - SMOKE AND MIRRORS. The Green puzzle gave them a set of binary numbers which told them which letter to use from previous puzzle answers (giving them the letters Y O A M), and the solution to the sudoku (LEVIATHAN) told them that these letters spelled out MOYA, which was the code for the bomb. In addition, the Blue coded messages from Spectrum also gave them this answer, as each of the messages was missing 2 crucial letters, which, when put together spelled CODE MOYA. But the teams didn't get that far!]

And finally the Purple puzzle gave them an instruction about how to find their objects. [note: originally they were going to have to find the items somewhere in the hotel but time issues prevented this.]
Purple solution: [REQUEST ITEM FROM AGENT AND TAKE TO CONTACT]

Fortunately for the fate of the planet, the players realised in time that the way to complete their mission was in fact not to give the items either to the Agency or to their contacts, but to keep them for safety.

And so the Mysteron plan was foiled and the Earth was saved. Curses.

[final note: during the course of the game, each team received six sheets of paper, coloured Red, Orange, Yellow, Green, Blue and Purple – in that order! - which should have suggested that Spectrum were somehow involved in this story. I don't believe any of the players actually picked up on this, even once they knew there were Mysterons involved...]

Detailed solutions to each of the puzzles are available here