And it wasn't because he was exhausted, which he was. Or because there was nothing left for him to do as FBI's al-Qaeda expert, the first case agent in New York on the 1993 World Trade Centre bombings and the man, it was often said, “who introduced bin Laden to America”. As the bureau’s special emissary without portfolio to the CIA and elsewhere in the US Government — as someone who knew what bits of information would actually be important in the battle against al-Qaeda — there was still plenty to do.

No he decided one night in mid-February 2003, that he had get home — immediately! — because of his tooth.

Or the lack of a tooth. It had been pulled, a wisdom tooth, on February 13 and he wasn’t healing. A “dry socket” is what the dentist called it when he went back a few days after the extraction. The gap in his gums wouldn’t fuse and scab, the way it usually works. So it had to be packed with gauze while the rest of his body was packed with Percoset.

But, now, five days later, on Friday night, as the digital clock screamed 2am, the drugs were turning against him. He was in some sort of narcotic, pain-addled swirl, pacing the one bedroom rental — a madman in briefs.

Then it came, a mystical, saving revelation. He had to get home. And then back to an old dentist near his home in New Jersey. He’d know what to do.

The roads were clear in the middle of the night — no one in either direction at 4am on the Jersey Turnpike. So he could drive in the only way that brought him a modicum of relief: head out the window, mouth open.

What followed were three weeks of dental hell. Getting the tooth packed every other day. Trying out new painkillers. Ranting around the house, driving his wife, Maureen, insane.

“Can you go back in, to do anything,” she asked one morning.

“Thure, there plenty I kud thu,” he said, through the gauze. “Thertainly.”

Being stationed at FBI’s headquarters in Washington since just after 9/11 meant that there wasn’t a whole lot to return to in New York. He didn’t really work there anymore.

But he drove his black FBI-issued Oldsmobile from Jersey through the Holland Tunnel to the enormous nondescript FBI office in southern Manhattan — a building in plain clothes — and into the underground garage. His parking spot was gone. No spots, anywhere. The guy who introduced bin Laden to America — thirty years with the bureau, and he’s doing quarters at a meter.

The office had changed. Offices do, quickly, with so much happening. But, it was nice to be back. Coleman’s a hero up here. John O'Neill, the FBI’s obstreperous al-Qaeda hunter, died in the 9/11 attacks. But Dan was still around.