Labyrinth

Hunting an old friend's killers, a professor-turned-spook unearths a conspiracy that threatens every person on Earth

An American op is murdered somewhere in the dusty wastelands of southern Colombia. His final transmission: a desperate warning that whatever he had stumbled upon is worth taking seriously. It is called Tantalus, and in two weeks it will be unleashed on the world.
Washington could dispatch the army, the commandos, or the CIA, but professional action will only send the men behind Tantalus under deeper cover. Instead, the

State Department chooses Christopher Locke, an old friend of the deceased. Once the Academy's strongest agent, he's an unemployed professor with crushing bills, three children, and no prospects. These are problems the government can solve.

All he has to do is get on a plane-and take his vengeance.