The Lost Symbol: In Which An Old Naperville Secret Is Revealled

Professor Hilary Langdon and her noble assistant Grumpy ran as fast as they could along the corridor.
"Where are we going?" asked Grumpy breathlessly.
"No idea, but we haven't run anywhere for a few minutes and it just seemed the right thing to do," Professor Langdon replied.
"Well I think we'd better stop now," said Grumpy. "We're on the roof of the Civic Offices and if we run anymore we'll fall over the edge."
"Good point," said the Professor. "Actually, I realize what our next step should be."
Rummaging in her pocket book, she pulled out a crumpled one dollar bill. Smoothing the back she saw the familiar symbol. An eye atop a triangle. Without faltering she folded the bill over and over.
"There! I have the answer," she told Grumpy.
"You do?" he said. "All you've done is make an origami swan."
"Yes, but if I unfold it like this, the lines make up a grid. Don't you see? Here, give me your laser. The one you use to make sure the lines are straight when you hang up a picture."
Grudgingly Grumpy handed it over. It was his favourite gadget, even though he'd never hung a picture straight in his life.
Professor Langdon pointed the laser out into the distance. A red beam of light leapt from building to building. It pointed the way from the top of the council offices to the bell at the top of the Moser Tower, down to the roof of Edward Hospital, back to pinnacle of St Peter and Paul Church.
"Wow. What does it mean?" asked Grumpy.
"It proves what I've always believed," replied the Professor. "That Naperville does indeed have a secret Red Light District."