Sophie arrived breathless outside the large wooden doors of the Salle des Etats—the room thathoused the Mona Lisa. Before entering, she gazed reluctantly farther down the hall, twenty yards orso, to the spot where her grandfather's body still lay under the spotlight.

　　The remorse that gripped her was powerful and sudden, a deep sadness laced with guilt. The manhad reached out to her so many times over the past ten years, and yet Sophie had remainedimmovable—leaving his letters and packages unopened in a bottom drawer and denying his effortsto see her. He lied to me! Kept appalling secrets! What was I supposed to do? And so she hadblocked him out. Completely.

　　Now her grandfather was dead, and he was talking to her from the grave.

　　The Mona Lisa.

　　She reached for the huge wooden doors, and pushed. The entryway yawned open. Sophie stood onthe threshold a moment, scanning the large rectangular chamber beyond. It too was bathed in a softred light. The Salle des Etats was one of this museum's rare culs-de-sac—a dead end and the onlyroom off the middle of the Grand Gallery. This door, the chamber's sole point of entry, faced adominating fifteen-foot Botticelli on the far wall. Beneath it, centered on the parquet floor, animmense octagonal viewing divan served as a welcome respite for thousands of visitors to rest theirlegs while they admired the Louvre's most valuable asset.

　　Even before Sophie entered, though, she knew she was missing something. A black light. Shegazed down the hall at her grandfather under the lights in the distance, surrounded by electronicgear. If he had written anything in here, he almost certainly would have written it with thewatermark stylus.

　　Taking a deep breath, Sophie hurried down to the well-lit crime scene. Unable to look at hergrandfather, she focused solely on the PTS tools. Finding a small ultraviolet penlight, she slipped itin the pocket of her sweater and hurried back up the hallway toward the open doors of the Salle desEtats.

　　Sophie turned the corner and stepped over the threshold. Her entrance, however, was met by anunexpected sound of muffled footsteps racing toward her from inside the chamber. There'ssomeone in here! A ghostly figure emerged suddenly from out of the reddish haze. Sophie jumpedback.

　　"There you are!" Langdon's hoarse whisper cut the air as his silhouette slid to a stop in front of her.

　　Her relief was only momentary. "Robert, I told you to get out of here! If Fache—""Where were you?""I had to get the black light," she whispered, holding it up. "If my grandfather left me a message—""Sophie, listen." Langdon caught his breath as his blue eyes held her firmly. "The letters P.S.... dothey mean anything else to you? Anything at all?"Afraid their voices might echo down the hall, Sophie pulled him into the Salle des Etats and closedthe enormous twin doors silently, sealing them inside. "I told you, the initials mean PrincessSophie.""I know, but did you ever see them anywhere else? Did your grandfather ever use P.S. in any otherway? As a monogram, or maybe on stationery or a personal item?"The question startled her. How would Robert know that? Sophie had indeed seen the initials P.S.

　　once before, in a kind of monogram. It was the day before her ninth birthday. She was secretlycombing the house, searching for hidden birthday presents. Even then, she could not bear secretskept from her. What did Grand-père get for me this year? She dug through cupboards and drawers.

　　Did he get me the doll I wanted? Where would he hide it?

　　Finding nothing in the entire house, Sophie mustered the courage to sneak into her grandfather'sbedroom. The room was off-limits to her, but her grandfather was downstairs asleep on the couch.

　　I'll just take a fast peek!

　　Tiptoeing across the creaky wood floor to his closet, Sophie peered on the shelves behind hisclothing. Nothing. Next she looked under the bed. Still nothing. Moving to his bureau, she openedthe drawers and one by one began pawing carefully through them. There must be something for mehere! As she reached the bottom drawer, she still had not found any hint of a doll. Dejected, sheopened the final drawer and pulled aside some black clothes she had never seen him wear. She wasabout to close the drawer when her eyes caught a glint of gold in the back of the drawer. It lookedlike a pocket watch chain, but she knew he didn't wear one. Her heart raced as she realized what itmust be.

　　A necklace!

　　Sophie carefully pulled the chain from the drawer. To her surprise, on the end was a brilliant goldkey. Heavy and shimmering. Spellbound, she held it up. It looked like no key she had ever seen.

　　Most keys were flat with jagged teeth, but this one had a triangular column with little pockmarksall over it. Its large golden head was in the shape of a cross, but not a normal cross. This was aneven-armed one, like a plus sign. Embossed in the middle of the cross was a strange symbol—twoletters intertwined with some kind of flowery design.

　　"P.S.," she whispered, scowling as she read the letters. Whatever could this be?

　　"Sophie?" her grandfather spoke from the doorway.

　　Startled, she spun, dropping the key on the floor with a loud clang. She stared down at the key,afraid to look up at her grandfather's face. "I... was looking for my birthday present," she said,hanging her head, knowing she had betrayed his trust.

　　For what seemed like an eternity, her grandfather stood silently in the doorway. Finally, he let out along troubled breath. "Pick up the key, Sophie."Sophie retrieved the key.

　　Her grandfather walked in. "Sophie, you need to respect other people's privacy." Gently, he kneltdown and took the key from her. "This key is very special. If you had lost it..."Her grandfather's quiet voice made Sophie feel even worse. "I'm sorry, Grand-père. I really am."She paused. "I thought it was a necklace for my birthday."He gazed at her for several seconds. "I'll say this once more, Sophie, because it's important. Youneed to learn to respect other people's privacy.""Yes, Grand-père.""We'll talk about this some other time. Right now, the garden needs to be weeded."Sophie hurried outside to do her chores.

　　The next morning, Sophie received no birthday present from her grandfather. She hadn't expectedone, not after what she had done. But he didn't even wish her happy birthday all day. Sadly, shetrudged up to bed that night. As she climbed in, though, she found a note card lying on her pillow.

　　On the card was written a simple riddle. Even before she solved the riddle, she was smiling. I knowwhat this is! Her grandfather had done this for her last Christmas morning.

　　A treasure hunt!

　　Eagerly, she pored over the riddle until she solved it. The solution pointed her to another part of thehouse, where she found another card and another riddle. ............