«I wanted to warn you, Mr. Langdon…» Sophie began, still catching her breath,» that you are sous surveillance cachée.Under a guarded observation.» As she spoke, her accented English resonated off the tile walls, giving her voice a hollow quality.

«But… why?» Langdon demanded. Sophie had already given him an explanation on the phone, but he wanted to hear it from her lips.

«Because,» she said, stepping toward him,» Fache’s primary suspect in this murder is you.»

Langdon was braced for the words, and yet they still sounded utterly ridiculous. According to Sophie, Langdon had been called to the Louvre tonight not as a symbologist but rather as a suspect and was currently the unwitting target of one of DCPJ’s favorite interrogation methods – surveillance cachée – a deft deception in which the police calmly invited a suspect to a crime scene and interviewed him in hopes he would get nervous and mistakenly incriminate himself.

«Look in your jacket’s left pocket,» Sophie said. «You’ll find proof they are watching you.»

Langdon felt his apprehension rising. Look in my pocket? It sounded like some kind of cheap magic trick.

«Just look.»

Bewildered, Langdon reached his hand into his tweed jacket’s left pocket – one he never used. Feeling around inside, he found nothing. What the devil did you expect? He began wondering if Sophie might just be insane after all. Then his fingers brushed something unexpected. Small and hard. Pinching the tiny object between his fingers, Langdon pulled it out and stared in astonishment. It was a metallic, button-shaped disk, about the size of a watch battery. He had never seen it before. «What the… ?»

«GPS tracking dot,» Sophie said. «Continuously transmits its location to a Global Positioning System satellite that DCPJ can monitor. We use them to monitor people’s locations. It’s accurate within two feet anywhere on the globe. They have you on an electronic leash. The agent who picked you up at the hotel slipped it inside your pocket before you left your room.»

Langdon flashed back to the hotel room… his quick shower, getting dressed, the DCPJ agent politely holding out Langdon’s tweed coat as they left the room. It’s cool outside, Mr.Langdon, the agent had said. Spring in Paris is not all your song boasts.Langdon had thanked him and donned the jacket.

Sophie’s olive gaze was keen. «I didn’t tell you about the tracking dot earlier because I didn’t want you checking your pocket in front of Fache. He can’t know you’ve found it.»

Langdon had no idea how to respond.

«They tagged you with GPS because they thought you might run.» She paused. «In fact, they hopedyou would run; it would make their case stronger.»

«Why would I run!» Langdon demanded. «I’m innocent!» «Fache feels otherwise.» Angrily, Langdon stalked toward the trash receptacle to dispose of the tracking dot.

«No!» Sophie grabbed his arm and stopped him. «Leave it in your pocket. If you throw it out, the signal will stop moving, and they’ll know you found the dot. The only reason Fache left you alone is because he can monitor where you are. If he thinks you’ve discovered what he’s doing…» Sophie did not finish the thought. Instead, she pried the metallic disk from Langdon’s hand and slid it back into the pocket of his tweed coat. «The dot stays with you. At least for the moment.»

Langdon felt lost. «How the hell could Fache actually believe I killed Jacques Saunière!»

«He has some fairly persuasive reasons to suspect you.» Sophie’s expression was grim. «There is a piece of evidence here that you have not yet seen. Fache has kept it carefully hidden from you.»

Langdon could only stare.

«Do you recall the three lines of text that Saunière wrote on the floor?»

Langdon nodded. The numbers and words were imprinted on Langdon’s mind.

Sophie’s voice dropped to a whisper now. «Unfortunately, what you saw was not the entire message. There was a fourth line that Fache photographed and then wiped clean before you arrived.»

Although Langdon knew the soluble ink of a watermark stylus could easily be wiped away, he could not imagine why Fache would erase evidence.

«The last line of the message,» Sophie said,» was something Fache did not want you to know about.» She paused. «At least not until he was done with you.»

Sophie produced a computer printout of a photo from her sweater pocket and began unfolding it. «Fache uploaded images of the crime scene to the Cryptology Department earlier tonight in hopes we could figure out what Saunière’s message was trying to say. This is a photo of the complete message.» She handed the page to Langdon.

Bewildered, Langdon looked at the image. The close-up photo revealed the glowing message on the parquet floor. The final line hit Langdon like a kick in the gut.

For several seconds, Langdon stared in wonder at the photograph of Saunière’s postscript. P. S. Find Robert Langdon.He felt as if the floor were tilting beneath his feet. Saunière left a postscript with my name on it? In his wildest dreams, Langdon could not fathom why.

«Now do you understand,» Sophie said, her eyes urgent,» why Fache ordered you here tonight, and why you are his primary suspect?»

The only thing Langdon understood at the moment was why Fache had looked so smug when Langdon suggested Saunière would have accused his killer by name.

Find Robert Langdon.

«Why would Saunière write this?» Langdon demanded, his confusion now giving way to anger. «Why would I want to kill Jacques Saunière?»

«Fache has yet to uncover a motive, but he has been recording his entire conversation with you tonight in hopes you might reveal one.»

Langdon opened his mouth, but still no words came.

«He’s fitted with a miniature microphone,» Sophie explained. «It’s connected to a transmitter in his pocket that radios the signal back to the command post.»

«This is impossible,» Langdon stammered. «I have an alibi. I went directly back to my hotel after my lecture. You can ask the hotel desk.»

«Fache already did. His report shows you retrieving your room key from the concierge at about ten- thirty. Unfortunately, the time of the murder was closer to eleven. You easily could have left your hotel room unseen.»

«This is insanity! Fache has no evidence!»

Sophie’s eyes widened as if to say: No evidence?» Mr. Langdon, your name is written on the floor beside the body, and Saunière’s date book says you were with him at approximately the time of the murder.» She paused. «Fache has more than enough evidence to take you into custody for questioning.»

Langdon suddenly sensed that he needed a lawyer. «I didn’t do this.»

Sophie sighed. «This is not American television, Mr. Langdon. In France, the laws protect the police, not criminals. Unfortunately, in this case, there is also the media consideration. Jacques Saunière was a very prominent and well-loved figure in Paris, and his murder will be news in the morning. Fache will be under immediate pressure to make a statement, and he looks a lot better having a suspect in custody already. Whether or not you are guilty, you most certainly will be held by DCPJ until they can figure out what really happened.»

Langdon felt like a caged animal. «Why are you telling me all this?»

«Because, Mr. Langdon, I believe you are innocent.» Sophie looked away for a moment and then back into his eyes. «And also because it is partially my fault that you’re in trouble.»