Nighthawk
"When the most advanced aircraft ever designed vanishes over the South Pacific, Kurt Austin and Joe Zavala are drawn into a deadly contest to locate the fallen machine. Russia and China covet the radical technology, but the United States worries about a darker problem. They know what others don't--that the X-37 is carrying a dangerous secret, a payload of exotic matter, extracted from the upper reaches of the atmosphere and stored at a temperature near absolute zero. As long as it remains frozen, the cargo is inert, but if it thaws, it will unleash a catastrophe of nearly unthinkable proportions"--