When it was still standing, 1906 Boone Street was a classic example of a Baltimore row house: three stories tall and only 15 feet wide, with a curved bay window in front and a narrow garden out back. Built in 1920, it featured a red brick facade, five bedrooms, and a claw-foot tub in the second-floor bathroom. Karen Saunders, who now lives two doors down, remembers living in the house as a child in the 1960s. Lewis Mitchell, a Coast Guard welder, purchased the house next door 21 years ago. Together with his brother, who lives one house over, Mitchell spent more than a year cleaning, painting, and repairing his new home. “I build ships,” Mitchell says. “I figured I could do a house.”

But even as Mitchell and his brother spackled walls and patched leaks, 1906 Boone sat vacant—a moldering eyesore that dragged the entire neighborhood down with it. Whenever it rained, water would collect in the abandoned row house and seep into Mitchell’s basement. To discourage break-ins, he hung his mother’s curtains in the upstairs windows at 1906. But with no one tending to it, the house eventually collapsed in on itself. When I visited the property, it looked like a stage set for an apocalypse film, its walls and floors partially demolished, its roof open to the sky. Bird droppings covered the stairwell. The bathtub was still there. Exposed, squatting precariously on a jagged scrap of what used to be the second floor, the tub felt somehow obscene: a ruin-porn image of a city in crisis.

In cities from Baltimore to Phoenix, vacant houses attract crime, serve as breeding grounds for rats and dumping grounds for trash, strain fire and police services, and gut local property values. “There’s a general reduction in quality of life around these properties,” says Kim Graziani of the Center for Community Progress, a nonprofit organization that studies run-down houses across the country and works to turn blighted properties into neighborhood assets. “You find increased rates of fear, anxiety, and depression among people who live adjacent to vacant and abandoned properties. There’s a loss of neighborhood fabric.”

One day, around eight years ago, Mitchell came home from the shipyard to find a piece of yellow plastic nailed to the front door of 1906 Boone, one of those FOR SALE—NO CREDIT CHECK! signs that have become ubiquitous in poor neighborhoods. Mitchell figured maybe he’d buy the house and fix it up, the same way he’d renovated his own home. But when he called the number on the sign, he didn’t reach a Baltimore resident who had inherited the place from his elderly parents, or even a local bank that had repossessed the house. Instead, he wound up talking to a woman from a company in Texas that offered to sell him the property for $30,000—nearly ten times what he thought it was worth. Whoever the real owner was remained a mystery.

The Community Law Center, a local legal services group, launched an investigation into 1906 Boone and hundreds of other vacant properties around Baltimore. The hunt took more than a year. In many cases, the identity of a property owner was hidden behind a maze of shell companies; an operation called Baltimore Return Fund LLC, for example, had purchased 1906 Boone at a city tax sale for $5,452. Eventually, the investigation revealed a Texas-based web of nearly a dozen LLCs—limited liability companies, a form of legal tax shelter—that controlled more than 300 properties in Baltimore. Nearly all had been purchased at tax sales, often online, between 2001 and 2010. Most sold for less than $5,000. Many were vacant and in bad shape.