– The driver was sweating as his white Kia pickup truck sped along a rain-slicked Baghdad highway toward a neighborhood bustling with open-air markets.

With every jolt and turn, his pulse quickened. Hidden in the truck's chassis was 1,100 pounds of military-grade explosives that the Islamic State of Iraq and Syria planned to use in an attack on New Year's Eve shoppers in the Iraqi capital.

A reckless driver on Iraq's chaotic roads might clip him, setting off the bomb. Or a clash could escalate at one of Baghdad's frequent checkpoints.

But there was another reason he was afraid. The driver, Capt. Harith al-Sudani, was a spy.

For the past 16 months, he had worked as a mole, posing as a jihadi in ISIS while passing information to a secret branch of Iraq's national intelligence agency. His record was stunning: He had foiled 30 planned vehicle-bomb attacks and 18 suicide bombers, said Abu Ali al-Basri, the agency's director. Sudani also gave the agency a direct line to some of ISIS'senior commanders in Mosul, Iraq.

A 36-year-old former computer tech, he was now, officials said, perhaps Iraq's greatest spy, one of a few in the world to have infiltrated the upper reaches of ISIS. But as he cruised toward his assigned target, he had a nagging suspicion that his cover had been blown.

Every day he remained embedded with ISIS was another day he risked his life. Today he had been caught in a small lie. If the half-ton of C-4 plastic explosive riding alongside him didn't kill him, ISIS might. Before he left on this, his penultimate mission, he sent his father a text.

"Pray for me," he said.

Little known outside of the highest levels of Iraqi and allied intelligence agencies, the Falcons have placed a handful of spies inside ISIS. The intelligence helped oust the extremists from their last urban strongholds last year and it now aids the hunt for ISIS leaders, like Abu Bakr al-Baghdadi.

Iraqi officials say the Falcons have foiled hundreds of attacks, making Baghdad the safest it has been in 15 years.

Basri credits the group's undercover work. "A drone can tell you who has entered a building but it can't tell you what is being said in the room," he said. "We can, because our people are inside those rooms."

Motivated by photos of children killed in ISIS attacks, Sudani became an undercover agent known as Abu Suhaib. His mission: Infiltrate an ISIS lair in Tarmiyah, a town near the intersection of two highways that was a hub for suicide bombers heading to the capital.

"He was the first of us to volunteer for such a mission," his brother Munaf said.

In weekly calls, a senior ISIS official in Mosul would order Sudani to meet suicide bombers arriving in Tarmiyah or to pick up a vehicle bomb.

Each time, he would alert the Falcons. Their task would be to intercept him and his deadly packages before they reached Baghdad.

A chase car would follow Sudani, using jamming equipment to block the signal to the bomb's detonator. His comrades would direct him to a place where they could disable the bomb. If he was transporting a bomber, they would lure him out of the car to be arrested or killed. Then the Falcons would stage explosions and issue fake news releases to keep Sudani's cover intact.

On Dec. 31, the Mosul commander told Sudani he had been chosen to take part in a series of bombings around the world.

Sudani picked up the white Kia. The plan began to unravel as soon as he veered off the main highway toward the Falcons' safe house. His phone rang. It was Mosul, asking his location.

Sudani assured the caller that he was en route to the target. The handler said he was lying. Sudani struggled to invent an excuse, saying he must have made a wrong turn. Spooked, he called his Falcons teammates and his brother Munaf, who was part of the chase team, directed Sudani to a new meeting point.

Eight agents dismantled the bomb, and in minutes, Sudani was parking the pickup at its intended location.

What Sudani didn't know was that ISIS had planted two bugs in the truck, allowing the extremists to hear his entire conversation with the Falcons.

In early January 2017, ISIS sent Sudani on another mission, to a farmhouse outside Tarmiyah. But by nightfall, the Falcons knew something was wrong. Because Tarmiyah was an ISIS stronghold, it took three days for Iraqi forces to mount a rescue operation. By then, there was no sign of Sudani.

For six months, the Falcons gathered evidence. In August, ISIS released a video showing militants executing blindfolded prisoners. The Falcons were certain that Sudani was one of them. "I don't need to see his face to know my brother," Munaf said.

In death, Sudani achieved a level of fame unusual in the shadow world of spies. Iraq issued a statement about his sacrifice for the nation.

But because his family do not have a body, they have been unable to obtain a death certificate, required to receive benefits due to fallen servicemen.

"I have a wound on my heart," said his father, Abid al-Sudani. "He lived and died for his country."