It has been called the most spectacular terror attack since 9/11. On the night of November 26, 2008, 10 men armed with guns and grenades launched an assault on Mumbai with a military precision that left 166 dead. India quickly learned the attackers belonged to Lashkar-e-Taiba, a Pakistani militant group associated with Pakistan's secretive intelligence agency, the ISI. But what wasn't known then was that a Lashkar/ISI operative had been casing the city for two years, developing a blueprint for terror. His name was David Coleman Headley, and he'd been chosen for the job because he had the perfect cover: he was an American citizen. FRONTLINE and ProPublica reporter Sebastian Rotella team up to investigate the mysterious circumstances behind Headley's rise from heroin dealer and U.S. government informant to master plotter of the 2008 attack on Mumbai.