From the book:
Katie slumped back on a stair. "I can't believe this is happening!" she said. "I can't believe Lester is missing!"
"Don't look now," George said. "But someone else is missing."
"Who?" Mari asked.
"Bess! " George replied.
"Bess?" Nancy gasped.
Her eyes darted around for her best friend. But George was right. Bess was gone!