* The setting is established: We are introduced to Greenwich, Connecticut, where a group of fourth-grade students, including Petra Andalee and Tom Shane, are attending an art exhibition featuring a Vermeer painting.
* The mystery begins: While looking at the painting, Petra notices a tiny, strange detail that she believes is a hidden message. She shares this observation with Tom, who is fascinated by the possibility of a secret code.
* The characters are introduced: We meet the two teachers, Mr. Van der Beek and Mrs. Silverman, who are both intrigued by Petra's observation but skeptical of its significance.
* A challenge is presented: Petra and Tom are challenged by Mrs. Silverman to investigate the painting and decipher the message, if there is one. They also find a note left by Mrs. Silverman in their mailboxes, hinting at a conspiracy.
* The story is set in motion: The discovery of the potential message and the mysterious note spark Petra and Tom's curiosity and set them on a quest to uncover the truth behind Vermeer's painting.
Chapter 1 serves to pique the reader's interest by introducing the main characters, establishing the setting, and presenting the central mystery that drives the plot. It also sets the tone for the book, which is a blend of suspense, friendship, and intellectual curiosity.