A hermetically sealed capsule
This hermetically sealed capsule once held a sample of the dangerous telepathic semi-intelligent mutagenic bacteria know as 'The Will of the Earth'. You stole it from Longbow for Vernon von Grun in an escapade you remember as :
The Great Grun Gathering
You'd worked with Vernon von Grun before, helping him to complete his basic research on the Devouring Earth, and was ready for the next big step. Vernon told you that he'd need several pieces that he couln't build himself for watherver it is he's planning. You were able to help get the first piece he'd need: A 'Telepathic Amplifier' you stole from the Council.
The next item Vernon needed was a bio-weapon dispersal device used for spreading out a bio-warfare agent. It took a lot of convoluted work, but in the end you managed to get one out from under the nose of the Malta Group.
The Last piece was a sample of the Will of the Earth mutagenic bacteria that was sealed off under Longbow guard. You still got the sample out of their base and back to Vernon. While he took the sample itself for his own mad schemes, he had no problem with you keeping the container it came in as a memento.