okay, I have found the plot:
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100th level Adventure: Time Collapse!
PCs: pre-generated characters.
Synopsis: A Chronomancer* (who was but 20th level), using wishes and chronomancy spells, created major time paradoxes which resulted in himself becoming a demi-god, but also creating a mess of dimensions and epochs. Now (inspired from the Amber novels), he resides in a castle at the junction of four planes and a dozen timelines. The world is slowly destroyed by this mess however, and is going to be soon obliterated in a giant sphere of anihilation (due to the time paradox and what not, this sphere is now growing fast, and if not stopped soon enough will devour the planet).
World Saviours: Nonetheless, this mess of dimensions and timelines also brought back immortal heroes of legend, at 100th level. So we get: The Lady of the Lake, Gilgamesh, Perseus the Immortal Warrior, Jesus the Ultimate Cleric, etc. Most probably these heroes weren't 100th level during their normal life, but they were all boosted to that incredible level of power due to the mess in the time and dimensions (handwaved explanation...).
So the PCs will first have to figure out what happens, then get to the mighty castle at the junction of planes and epochs. Of course, other epochs mean they will have to fight villains from the future (with modern weapons) as well as from the past.
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So here it begins. I have some old homebrewed adventures I could throw in. I could borrow some epic monsters somewhere on Enworld. Well...
(*: There is netbook on this subject, on my d20 Download website)