They stole Pandora's Box from a top secret military installation in the Althosian system and took it to the seventh planet in that system. They were told it would be used to create an opening to another dimension which had large amounts of the valuable drug Dream B.
This was only partly true. The Fellowship wanted the opening, but only as a means to allow the Yssgaroth into our universe. After the plan was stopped by Spike blowing up the machinery that was connecting to the other dimension, Swarf was caught and killed by a Hunter. (PROSE: The Pit)