The story, which was set 20 years in the future, was built up around a climactic battle that would settle which faction would dominate the Earth. It was pitched as a stand-alone maxi-series, similar to Wolfman/Perez's Crisis on Infinite Earths.
Moore's Central Plot:
This is the main central plot of Twilight, being the story that [Rip] Hunter tells Constantine and that Constantine passes on to the other parties involved, and it deals with the world of the Twilight. I don't have it broken down issue by issue or anything, but the rough shape is something like this: In the middle 1995 or earlier, when society was starting to break down, many of the villains on Earth tried to take advantage of this situation by exploiting the uncertainty and disaster. Incensed by this, the current Justice League decide to go on the offensive for the first time and plan a careful campaign that will remove all the super-villains forever. They enlist the aid of a lot of other superheroes in this, and they are mostly very effective. So effective, in fact, that they begin to be seen as the only effective force for reason and order in a fast crumbling world.
This goes to the assembled heroes' heads a little, and in an attempt to secure their new power base they pass a majority motion outlawing aliens from Earth. While this is passed and is rigorously enforced, it is one of the decisions that causes the first serious rift in the ranks of the assembled super-doers, with some small groups like the Titans starting to drift away from the main group. This process continues until the state of the ruling Houses is pretty much as described above, with the House of Secrets containing the only super-villains to survive the purge other than those who reformed, and the House of Lanterns demolished upon Earth and temporarily relocated upon Mars pending the planned secret invasion.
At the start of our story proper, there is quite a lot of different activity going on in the various camps. The Houses of Steel and Thunder, each suffering their own internal stresses, are preparing for the marriage of the delinquent Superboy with Mary Marvel Jr., daughter of the Captain and Mary Sr. This is a development that causes considerable anxiety all over the place: previously, even the two most powerful Houses could not attempt to exert any pressure upon the others for fear that the other Houses would unite against them. Both Houses knew that individually they couldn't hope to take on the assembled might of the Titans, Justice League and others. This preserved a status quo of sorts.
However, with the prospect of an alliance in the offing, it seems quite possible that the assembled forces of three people with the power of Superman, four people with the power of Captain Marvel and Wonder Woman into the bargain could easily smash the most firm resistance. This prospect worries both the Houses of Titans and Justice tremendously. It also worries the villains remaining at the House of Secrets who remember back to the purges of the nineties and shudder. It certainly alarms the people living in the barrio, who, though downtrodden, still have a certain amount of liberty, impoverished though it be, and are not actually living under the absolute dictatorship that could result from a marriage between the Houses of Steel and Thunder.
The other major party alarmed by the prospect are the assembled alien forces that are conspiring out on the moon of Mars. They don't like the thought of a planet ruled by an unstoppable superhuman elite purely because it might very quickly pose a threat to the aliens' own well-being. Their plan is cryptic, but we learn a bit of it at a time. The main thrust of their plan is that they intend to use Adam Strange's place as their agent on Earth to set up a Zeta Beam link through which an inviting army of Hawkpeople, super-powered green Martians and members of the Green Lantern Corps could materialize in the center of Times Square or somewhere, this plan being linked to a Thanagarian Plan that has to be abandoned in the current issues of Swamp Thing, resurrected here to much more spectacular purpose.
Alan Moore ends his pitch with the following comment:
"I hope you can see how it's meant to fulfill all the requirements mentioned earlier. There are opportunities for new characters to get a springboard, old characters to get a shot in the arm and all the merchandising you can handle in terms of games and stuff, at least as I see it. The warring Houses idea sounds ideal for role-playing games, or maybe even a video game. The overall continuity is hopefully enhanced without being damaged in any irreversible way, and I think we might get a damn good yarn out of it in the bargain. Anyway, I seem to have gone on far longer than I intended, so I better wrap this up. I'll be looking forward with interest to hearing what any of you have to say about all this when you've had a chance to read it. If any sections are incomprehensible and need clarifying then please give me a call."You can find the full text of the proposal here: http://fourcolorheroes.home.insightbb.com/twilightfree.html