The last time Robert Caro set foot in Robert Moses’ office, Moses abruptly ended their interview and never spoke to him again. On a bright morning last week, Mr. Caro, 80, climbed into the back seat of a rented Toyota Camry to visit that office for the first time in 48 years.

In the interim, Mr. Caro’s biography of the public works titan, “The Power Broker: Robert Moses and the Fall of New York,” which he wrote for an advance of $5,000, has had 49 printings and was recently bought for publication in China, where it has been available in unauthorized editions.

In the front seat of the car sat the prime minister of the Netherlands.

“Hi, I’m Mark,” said the prime minister, Mark Rutte.

Mr. Rutte and his friend Koen Petersen, a historian and coffee company executive, had invited Mr. Caro to lunch last year and asked if he would someday show them some sights from the book. They said they visited the city every year with a copy of “The Power Broker.”

“We’re like groupies,” Mr. Rutte said. ...