Story Highlights:  It's not yet Halloween, but old ghosts are coming back to haunt. About a month ago (yes, only a month ago, though by now it feels like ages), the US government chose not to save Lehman Brothers from failure—perhaps believing its failure wouldn't cause as much systemic damage to the financial system as other "too big to fail" institutions (dubious, but possible). Ironically, Lehman's failure proved to be a huge test to the financial system, specifically to the $55 trillion credit default swap (CDS) market. (Recall: This is precisely the market many believed sunk AIG in the first place.) CDS contracts are purchased by holders of debt to insure against the event of that debt defaulting. Dealers selling the contracts agree to pay the buyer the face value of the debt security if default occurs.