What is the Infinite Abyss? Where can I get it?

For this version you don't need to buy Descent 2 and Vertigo Series seperately. Infinite Abyss contains:

At the moment there is nearly no shop which offer this Series. You must order it directly from Interplay. You find nearer informations how to order it on the Interplay website: http://www.interplay.com !

If you already have Descent 2, then the Veritgo Series are the right to buy!