McCabe said: “This is an up-and-coming area. It looks like nothing, you know — but you put a bit of paint on the brickworks, smarten the place up, and all of a sudden it becomes a spot for little boutique stores or the up-and-coming D.J.s. You’ve got warehouse conversions; you’ll see guys coming out of the buildings in the morning — suit-and-tie, briefcase. If you’re driving a cab, you could pick someone up in the City at the end of the day heading back this way.”

McCabe had spent his entire professional life in the building trade. He’d worked alongside his father, an electrical engineer, and then as the owner of his own small firm specializing in roof maintenance, steel work and asbestos removal. He liked the work, but it was grueling — 15-hour days, seven days a week — and the £50,000 ($80,000) he took home wasn’t enough, to his mind, to justify the sacrifices. A job as a taxi driver seemed an attractive alternative. London cabbies are self-employed businessmen who set their own schedules. The metered fares of taxis are high, and drivers keep what they earn. The overhead — the cost of gas and of owning or leasing a taxi — can be steep, but cabbies who put in the hours can make a good living. There are no official statistics, but drivers themselves will tell you that London cabbies can earn around £65,000 per year, about $100,000, while maintaining an enviably flexible schedule. As a cabbie, McCabe figured, he could work seven, 10, 15 days straight — and then take four days off to spend time with his wife Katie, a hairdresser, and their children, Archie, 4, and Lulu, 3. He sold his engineering outfit and devoted himself full-time to the Knowledge, living off the savings he’d gained from the sale of his business.

It was now 37 months since he’d paid the £525 enrollment fee to sign on for the test and appearances. “The closer you get, the wearier you are, and the worse you want it,” McCabe said. “You’re carrying all this baggage. Your stress. Worrying about your savings.” McCabe said that he’d spent in excess of £200,000 on the Knowledge, if you factored in his loss of earnings from not working. “I want to be out working again before my kids are at the age where someone will ask: ‘What does your daddy do?’ Right now, they know me as Daddy who drives a motorbike and is always looking at a map. They don’t know me from my past, when I had a business and guys working for me. You want your life back.”

The Knowledge is notorious for snatching away lives, and for putting minds in a vise grip. “Everything becomes about the Knowledge,” McCabe said. “My wife will be talking to me about plans or the kids, and it’s not even registering what she’s saying. Because all I’m thinking is, ‘I can’t turn right into that road in Hammersmith, can I?’ If you read the paper, or watch the news or a film, you’re looking at the background. ‘Oh, I know that road there.’ ”

McCabe said that he dreamed about the Knowledge: sometimes exhilarating visions of zooming through London streets, more frequently nightmares about unfamiliar roads or disastrous LTPH appearances. Often, McCabe would wake in the middle of the night and hurry downstairs to study the map. In his dining room, there were three maps: two jumbo London street plans — one laminated on the dinner table and one tacked to the wall — and an enlarged view of the W1 postcode, the bustling zone which stretches south from Marylebone to Piccadilly and east to Soho. McCabe had ledgers he’d filled with jottings on topics like “Small and Awkward Squares.” There were also flashcards that McCabe had made up, listing a point on one side (“Tooting Mosque, SW17”) with information about its location and navigation on the other (“Gatton Road, one way, access via Fishponds Road”). McCabe stacked the cards in piles of 300; he had 40,000 in all. His home, he said, had become a library of the Knowledge.

But book-learning gets you only so far. “You’ve got to get out on the bike,” McCabe said. When he was doing Blue Book runs, McCabe would ride the streets all night, leaving when his wife got home from work at 9 p.m. and returning at 4 in the morning. Pointing, McCabe told me, can be “very cold, very lonely, very dangerous.” One night, McCabe was out pointing on his motorbike when a driver slammed into him from behind. McCabe went over the roof of the car, but suffered just a few scrapes and bruises. The bike was totaled. “I’m stationary in the filter lane, and the car just came around the bend and hit me,” McCabe said. “This was on a road called Pound Lane. Right across from the fire station at the corner of Harlesden Road.”