Emily thinks it had to be Charlie. James isn’t sure. They decide it is time to talk to Mr. Quisling. Later, when Emily looks up the quest thread between Coolbrith and Mr. Quisling, it has disappeared. She deduces that Coolbrith must have deleted the thread and was using the quest to make Mr. Quisling look responsible for the fires. She thinks about the unbreakable code and wonders how they will get to Gull Island. She remembers that Ms. Linden mentioned having a boat. She leaves Ms. Linden a message asking about it.

Emily frets over what to say to Mr. Quisling. She asks Matthew for advice, and he encourages her to just start talking. Emily gets ready for the dance and puts on her scrabble tile costume. As she is about to leave, another Book Scavenger alert chimes. Coolbrith has hidden a new Tom Sawyer at her school.

Emily and James hurry to school, worried about Coolbrith. Students arrive in their costumes and prepare for the presidential games. Emily spots Charlie setting up his DJ equipment and looks for any suspicious behavior. He seems entirely focused on his role as DJ. They see no sign of Mr. Quisling. Maddie sees Emily watching James with worry. Maddie reveals that she used to like James but says she doesn’t anymore, so Emily shouldn’t worry. Emily sees James as a close friend, not a love interest. Emily finally sees Mr. Quisling arrive by a side door. Before she can get to him, she runs into Mr. Griswold. She and James excitedly greet him. Mr. Quisling comes to talk to them, recognizing Mr. Griswold and growing shy in his presence. Mr. Quisling explains that Book Scavenger has helped him repair his relationship with his son. Just as Emily is about to say something to Mr. Quisling, Vivian announces the start of the game. When she calls on Emily to tell everyone the rules of the game, Emily freezes. Mr. Griswold admits that he is afraid of public speaking too and encourages her to focus on the friendly faces in the audience. Emily suddenly asks Mr. Quisling whether he has done any book hunting tonight, and he replies that he is only here to chaperone the dance. Emily finally steps up to the mic and introduces her game as people cheer.

Emily explains the rules and feels relieved that nobody heckles her or laughs. Emily stands with Team Teddy Roosevelt. Emily races through the obstacle course and her team comes in second, meaning they have to face off against Team Abraham Lincoln in the balloon stomp. Emily notices everyone laughing, including Mr. Griswold, Mr. Sloan and even Mr. Quisling. Emily doesn’t even are when Nisha stomps her balloon because everyone is having so much fun. Mr. Griswold congratulates Emily and James and leaves feeling inspired. Emily tries again to talk to Mr. Quisling but he runs off to pick up a fog machine. James suggests they try to have fun for a while and enjoy the dance. As they dance, Mr. Quisling returns with a large jug and pours it into the fog machine. This is the last thing Emily remembers before the fog machine explodes.

The fog machine makes a series of popping sounds and starts to smoke. Emily shouts “fire,” and the crowd in the gym slowly realizes that they need to get out. Emily feels triggered immediately and starts coughing. Outside, students mill around and walk home in disarray. Emily and James know it was Coolbrith. They think Charlie is behind it all since he brought the fog machine. The cops take Mr. Quisling for questioning. Emily and James worry Mr. Quisling has been framed to look responsible. Charlie has disappeared. Emily and James plan a way to get inside the building to talk to Mr. Quisling.

Emily and James sneak around to a side door. As they hurry through the empty halls, they hear a long creak and hide. They hear the cops interrogating Mr. Quisling and pointing out all the planted evidence making him look guilty. Emily finally speaks without second-guessing herself. She tells Mr. Quisling and the police that Mr. Quisling is being set up by Coolbrith. She and James tell the police they think Charlie is behind the fires because he hates Mr. Quisling for giving him a D. Mr. Sloan appears in the doorway to escort the kids away. He mentions that Emily must be triggered since she was in Hollister’s store when the fire happened. Emily doesn’t know how Mr. Sloan would know she was in the store at the time. Emily realizes that Mr. Sloan is Coolbrith. Mr. Quisling finally recognizes Mr. Sloan as a former friend of Miranda’s who used to go by his full name, Harvard Sloan. Mr. Sloan claims that Mr. Quisling ruined his life. Mr. Sloan accidentally created a fireball during an experiment gone wrong, and he blames Mr. Quisling for his firing. The police escort Mr. Sloan away.

Mr. Quisling reveals that he has been trying to figure out Coolbrith’s identity for some time. First, he thought it was his son. Then he thought it was his old friend Miranda, who loved the poet Ina Coolbrith. He hadn’t even remembered Mr. Sloan. They figure Mr. Sloan didn’t even care about the unbreakable code but simply used it to entice Mr. Quisling. Emily and James rush out front to find their parents, who must be worried. Emily spots her dad and gives him a huge hug. James is surprised to see that his dad came back from his business trip a day early and is there to pick him up. Before they leave, Emily and James tell Mr. Quisling that they solved the unbreakable code. They invite him to meet them at the History Center.

Emily is so tired after everything that she falls asleep in her Scrabble costume. As she goes to the bathroom, she overhears her parents talking about moving the family again. Emily doesn’t talk to her parents all morning. Just as she is about to leave, her dad sits her and Matthew down for a family talk. Emily refuses to hear him out and leaves with James. Matthew convinces Emily to let him accompany them.

Emily and James show Matthew, Mr. Quisling, and Ms. Linden the cracked code. Ms. Linden offers to take them to the island in her boat as long as all the parents give permission. Emily worries her parents won’t agree to it. Emily asks her parents to join the boat trip, knowing they won’t turn down a spontaneous adventure. Mr. Quisling and Ms. Linden start to hit it off and bond over their tattoos. Emily fills her parents in on the story of the unbreakable code. When they get near enough to Gull Island, Emily, James, and Mr. Quisling row to shore in the dinghy with a metal detector. The island is indeed covered in gulls and bird poop. Mr. Quisling spots a rock that looks like a duck, and they find the third tree. The metal detector beeps. Mr. Quisling starts digging with a shovel through layers of bird poop until he hears a clank. They pull out a tin can and find a small, sooty, black bowl inside it. Mr. Quisling rubs at the soot, revealing a patch of gold.

Emily and James hop around with excitement until Mr. Quisling informs them that the owner of the island will be the owner of the treasure. Emily blinks back tears and admits that she hoped the bowl would help pay for life in San Francisco so they wouldn’t have to move again. Emily’s dad reveals that the news he wanted to share is that he was offered a job at Bayside Press. Emily happily hugs him.

A week later, Emily and her family gather around the TV to watch the newscast about the treasure discovery. She learns that due to antagonism toward Chinese people during the Gold Rush, Chinese miners would sometimes melt down the gold they found into everyday objects like bowls and cover them in soot.

Emily and James head to Hollister’s to help repaint along with Mr. Griswold, Mr. Quisling, and the whole dance committee. Charlie has been fired because it turns out he lied about knowing how to code for Hollister’s website and had run to his car to check a how-to manual on the day of the fire. Hollister pulls out It’s-Its for everyone.

After finding the bowl, they notify the island’s owner, and he donates the bowl to the Chinese Historical Society and awards Emily and James each a $10,000 finder’s prize. Emily’s parents insist she keep the money, and James’s father refuses the money as well, promising to cut down on business trips. They both offer their money to Hollister to help get the store up and running. Hollister refuses them and insists they keep it. He announces a new partnership with Mr. Griswold. Mr. Griswold has a big plan for a Book Scavenger escape room event on Alcatraz Island. They will auction off tickets and use the funds to help Hollister’s bookstore. Emily feels hopeful and excited.