“O happy town beside the sea,” philosopher Ralph Waldo Emerson called Boston, “whose roads lead everywhere to all.” Friday would have saddened him. Oliver Wendell Holmes preferred to call Boston “the hub of the solar system.” But while the planets spun in their orbits, the hub fell ominously silent, its roads as empty as the day after Armageddon.

Silent, that is, but for the throbbing of military helicopters through otherwise vacant skies, and the whine of police sirens. An entire city, one of the great cities—a hive of finance and technology and commerce and culture—was made eerie and ghostly in the blink of an eye. And somewhere in the midst of this unnatural, perhaps unprecedented, scene, the cause of it all lay hidden.

A teenage boy.

Dzhokhar Tsarnaev, ruiner of so many promising lives, including his own, had vanished after allegedly participating in his second spree of terror in four days. The accused Boston Marathon bomber, a slim, doe-eyed athlete of 19, was flushed from anonymity on Thursday evening, when the FBI released images from surveillance videos that placed him with his brother, Tamerlan, at the scene of Monday’s mayhem. The hunted pair apparently left their apartment in Cambridge, killed a campus policeman nearby, stole a car, and fought a little war with their police pursuers in the nearby suburb of Watertown. Some 200 shots were exchanged, and the brothers lobbed homemade grenades. Tamerlan was mortally wounded in the battle, while his younger brother ran into the night.

When dawn approached and the fugitive still had not been found, Massachusetts Gov. Deval Patrick and Boston Mayor Thomas Menino decided to shut down the city. They started with public transportation. Commuter trains and subways were switched off. Bus service was suspended. Amtrak stopped running, and ferries remained at their piers. As Richard A. Davey, secretary of transportation for the Bay State, explained: “We did not want to have customers potentially put in harm’s way. And we didn’t want to give this suspect the opportunity to get out of the city using public transit.”

Spots of blood on the Watertown pavement suggested that the second suspect was still nearby. Officials took the larger step of asking citizens throughout Boston to hunker down in their homes—“shelter in place,” in the lingo of this awful age of terror. Citizens would be safer behind locked doors, they reasoned, and if the streets were empty, police would be free to focus their efforts on the hunt. Lights went out in the offices of businesses great and small. Guards locked the spinning doors of downtown skyscrapers. School was cancelled. At Fenway Park, the Red Sox game was postponed; ditto the Bruins game at the Garden.

Behind bolted doors, Bostonians saw through their windows things never before seen on a warm Spring day in Beantown. Normally snarled and honking thoroughfares like Summer Street and Commonwealth Avenue were empty. The Boston Common and Quincy Market were deserted. The winding streets of the North End had hardly any map-squinting tourists blocking the sidewalks. No racing shells skimmed along the Charles River; the lawns of Harvard were quiet and lonely; no pot smoke scented the Square.

“How can one person cause all this?” asked Joan Kraus, a Watertown native.

And where was he? SWAT teams went door-to-door through Watertown, where one homeowner after another peered out to see who was knocking before turning the latch. “When I opened the door, there were three police officers in fatigues standing there with huge guns, pointing into our house and at me,” said Jennifer Sartori, a professor at Northeastern University. “I know these people are here to protect me, but I have never stared into the barrel of a gun before, and I hope I never have to again.”

Detectives combed through the brothers’ apartment, and others canvassed the University of Massachusetts campus in Dartmouth, miles to the south, where the younger one had reportedly been enrolled. Blackhawks flew low over tense neighborhoods while patrolmen flagged down the few remaining taxicabs to peer into backseats.

After so much trauma this week, many parents tried to shield their children from the sight of dark, growling armored personnel carriers rolling slowly along neighborhood streets; of armored men in goggled helmets aiming automatic rifles; of fierce-looking dogs straining at short leashes. The city held its breath as the nation watched and waited.

On this same day 238 years earlier, British troops from Boston reached the town green in nearby Lexington, where the waiting Minutemen fired “the shot heard ‘round the world.” Now, the metaphor was a reality, as satellites beamed images of Boston around the planet. Yet the story was the unheard shot from the unseen gun of the unfound terrorist who had shut down a great city.

As the sun slid down the sky, Gov. Patrick and Mayor Menino at last acknowledged just how wrong this all was, and how vain. Dzhokhar Tsarnaev remained at large, but they would no longer allow him to hold the city prisoner. The officials ended the voluntary lockdown of the happy town beside the sea, and reopened the streets with a sensible warning to be careful out there. The Hub began to turn again.

Set free, a homeowner in Watertown went outside and made his own little search. He found suspicious signs of an intruder hiding in his trailered boat behind the house. Infinitely more useful than he had been all cooped up, this citizen called the police. He had cracked the case.

As the authorities arrived, Boston was already returning to life. In short order, they took their prisoner, a mere boy, frightened, cowering, and alone.