Falls The Shadow

In the near future our planet is exhausted. But there is a dramatic solution: start again. But where?
A select group of scientists know how to travel to a parallel universe and there they set up a small community on the parallel planet Plenor.
Hundreds of years and a number of generations later, Earth still survives and visiting the Old World is for educational purposes only.... unless someone gets close to discovering Plenor - then action has to be taken to protect it.
Plenor's utopian life is about to be disturbed...