Mark Lane is a quiet residential side street in Milton with manicured lawns, midpriced cars parked in driveways, and few people out and about. Near one end of the road is a gray, ordinary-looking house with a curving driveway and shades drawn on its many windows.

But on Labor Day weekend, the street was crammed with more than 350 cars, police said, and behind the home, in a nearly 6,000-square-foot pool house hidden from the street view, it was chaos.