IN 1941, Edward Hopper began what would become his most recognizable work, one that has become an emblem of New York City. “‘Nighthawks,’” Hopper said in an interview later, “was suggested by a restaurant on Greenwich Avenue where two streets meet.” The location was pinpointed by a Hopper expert, Gail Levin, as the “empty triangular lot” where Greenwich meets 11th Street and Seventh Avenue, otherwise known as Mulry Square. This has become accepted city folklore. Greenwich Village tour guides point to the lot, now owned by the Metropolitan Transportation Authority, and tell visitors that Hopper’s diner stood there. But did it?

Not long ago, one of the readers of my blog, Vanishing New York, sent in an old photo of the lot. There was no diner, only an Esso gas station and a White Tower burger joint that looked nothing like the moody, curved, wedge-shaped lunch counter in “Nighthawks.” An urban mystery had just revealed itself: If the diner wasn’t in the empty lot, then where was it?

Being an obsessive type, prone to delve, I began searching for Hopper’s diner with the help of two of my readers. Multiple streets converge at Mulry Square, creating a shattered-glass array of triangular corners. The buildings wedge themselves into these tight angles, bricks tapering to near points, each structure bearing a Hopperesque resemblance.

I snapped photos of every possibility and checked them against their ancestral images in the New York Public Library’s Digital Gallery. I made a trip to the city’s Municipal Archives, where I scanned the 1930s atlases of Manhattan known as “land books,” matched block and lot numbers to scratchy rolls of microfilm and scrolled through muddy 1940s tax photos. Slowly, I began ruling out suspects.