Silas gazed upward at the Saint-Sulpice obelisk， taking in the length of the massive marble shaft. His sinews felt taut with exhilaration. He glanced around the church one more time to make sure he was alone. Then he knelt at the base of the structure， not out of reverence， but out of necessity.
The keystone is hidden beneath the Rose Line.
At the base of the Sulpice obelisk.
All the brothers had concurred.
On his knees now， Silas ran his hands across the stone floor. He saw no cracks or markings to indicate a movable tile， so he began rapping softly with his knuckles on the floor. Following the brass line closer to the obelisk， he knocked on each tile adjacent to the brass line. Finally， one of them echoed strangely.
There's a hollow area beneath the floor！
Silas smiled. His victims had spoken the truth.
Standing， he searched the sanctuary for something with which to break the floor tile.
High above Silas， in the balcony， Sister Sandrine stifled a gasp. Her darkest fears had just been confirmed. This visitor was not who he seemed. The mysterious Opus Dei monk had come to Saint-Sulpice for another purpose.
A secret purpose.
You are not the only one with secrets， she thought.
Sister Sandrine Bieil was more than the keeper of this church. She was a sentry. And tonight， the ancient wheels had been set in motion. The arrival of this stranger at the base of the obelisk was a signal from the brotherhood.
It was a silent call of distress.