Robin and Hercules trade blows on the bridge for 10 minutes without either gaining ground. Billy ends the standoff by warning that the noise might attract the Sheriff, then pointing out the obvious: Hercules is stronger. Immediately, Hercules seizes Robin’s staff and throws him into the river. Robin concedes graciously, and the two express mutual admiration. Billy suggests Hercules join Robin’s group; Marian invites both Hercules and Billy, calling the group “the merry people” rather than “the merry men.” Billy is quietly moved, since classmates never choose him for teams. The Sheriff of Nottingham immediately rides in on a black horse.

The Sheriff, a sour, gaunt figure dressed entirely in black, announces he’s found his quarry. When Robin confirms that Billy has joined the outlaw band, the Sheriff declares the alliance treason and sentences Billy to death. Maid Marian responds by hurling her dagger into the Sheriff’s thigh. As the Sheriff screams in pain, the others urge Billy to run, and he does.

In Lab Note 320, Dr. Xiang Libris notes that Billy’s intensifying fear may cause him to abandon the project. To keep him engaged, Dr. Libris plans to send a message through pneumatic tubes along the lagoon.

Billy reaches the lagoon breathless, wondering whether a fictional character can actually kill him and whether he has accidentally “rewritten literary history” by persuading Hercules to join Robin’s band. Near the rowboat, he spots a green bottle containing a note that promises great treasure is hidden on the island. He resolves to find the treasure in the hope that his parents will stop fighting over their finances.

At the dock, he meets Walter, a boy playfully casting pretend spells with a Junior Wizard trading card from a game called Magical Battical. Walter uses an asthma inhaler and freely admits to being bad at keeping secrets, tying knots, and rowing. He invites Billy to a local restaurant called the Red Barn and promises to share what he knows about Dr. Libris.

Billy visits Walter’s eclectic family home, the Hodgepodge Lodge, which is redesigned each summer by Walter’s engineer father. Biking to the Red Barn, Walter relays Dr. Libris’s claims about the ornate bookcase in the study: It once belonged to Charles Dickens, some shelves came from Scheherazade’s trunk, and Geppetto carved its decorations.

At the Red Barn, the boys share waffle fries and order a pie for Billy’s mother. A plaque on the restaurant’s wall honors Dr. Libris for donating the island as the Lake Katrine Bird Sanctuary. When Billy asks about the wire dome, Walter explains it contains birds and adds that his father helped build it for a classified government project. Billy considers how this might explain the cabin’s security cameras and satellite dish.

On a shortcut back through the woods, Billy and Walter are blocked by Farkas and the two other bullies, who demand payment for use of the path. Farkas eyes the pie in Billy’s basket. Inspired by the heroes he met on the island, Billy hatches a plan. He says he’ll give the bullies the pie in exchange for Walter’s freedom. Farkas agrees, and Walter rides ahead. Once Walter is safely away, Billy claims his mother can see them, causing all three bullies to turn away. Billy escapes while Farkas shouts threats.

Back in the cabin, Billy brings Walter into the study and has him read The Three Musketeers silently for 10 minutes. Walter hears nothing unusual. When Billy reads the same sword-fight passage himself, he hears clashing blades and French-accented voices, but Walter hears only a bird outside. Billy hopes that Walter will be able to see the characters he met, and he reveals that the skeleton key also opens the gate on the island. Walter immediately sprints for the dock.

After a 20-minute row, the boys reach the island. Under the dome, Walter can hear sword fighting, and both hear a voice saying D’Artagnan’s name. The clearing has become a cobblestone Parisian square, where the Three Musketeers and D’Artagnan are drinking at an outdoor café after defeating Cardinal Richelieu’s guards. Walter comically confuses their names with candy bars.

In Lab Note 321, Dr. Libris confirms that the promise of treasure successfully brought Billy back to the island. He notes that Walter, his neighbor of 10 summers, can also perceive the characters generated by Billy’s imagination while under the dome. Dr. Libris views this as proof that theta waves produce tangible results, bringing the project one step closer to profitability.

Billy smiles as he approaches the musketeers, and D’Artagnan takes this as an insult. Walter jokes about cardinals, the birds, and the musketeers take this as another slight because they oppose Cardinal Richelieu. D’Artagnan challenges the boys to a duel. Before he can strike, Robin Hood, Maid Marian, and Hercules emerge and attempt to rob the musketeers. All seven armed characters end up circling the boys. To stop a fight from breaking out, Billy has Walter read his Junior Wizard trading card. A small wizard materializes and scatters golden glitter over the group, sending every fictional character to sleep. The wizard vanishes, and Billy and Walter escape.

Rowing back, the boys try to make sense of the island. Walter notes that the Junior Wizard came from a trading card rather than Dr. Libris’s bookcase, complicating Billy’s theory that the strange appearances come from the books. Billy rejects Walter’s suggestion that the characters are played by actors, arguing the events are too instantaneous to stage. He presents his mother’s dissertation subject, parallel universes, as a possible explanation. Walter half-seriously proposes they’re both dreaming. Billy refuses to abandon the adventure or the treasure, and he shows Walter the note he found in the bottle.

The next morning, Walter comes to Billy’s cabin with a shovel. Inside the study, Walter notices the tin ceiling and proposes it could harvest brain signals, relaying them through the satellite dish and an underwater cable, which his father’s crew installed years earlier, to project images on the island. Billy hadn’t known about the cable. Walter also cautions Billy away from The Time Machine. Billy reveals that Treasure Island is absent from the bookcase and presents The Adventures of Tom Sawyer as a substitute guide on treasure-hunting. After Billy reads a passage and hears a clock strike 10 times, both boys race to the dock.

Billy and Walter arrive at the island with shovels. Walter has secretly tucked Pollyanna: The Glad Book into his waistband, hoping to summon a safe character unlike the armed figures they’ve encountered. The Parisian square is gone, replaced by an elm-lined country lane. Walter realizes the slumber spell only lasts about an hour. Propping their shovels against a stone column, the boys head up the lane and find WANTED posters on every tree bearing the names of Robin Hood and Sir William of Goat, signed by the Sheriff of Nottingham.

A cheerful girl named Pollyanna appears and explains her glad game, which involves finding something positive in any situation. She cheerfully notes that the poster makes Billy “nearly as famous as Robin Hood” (114). She tells them Robin’s group is heading to the Saint Petersburg Sunday School Picnic and Archery Contest, where the grand prize is a solid gold arrow. Billy immediately reads it’s a trap: The Sheriff is using the prize to draw Robin into the open. Feeling responsible because Marian wounded the Sheriff to protect him, Billy asks Pollyanna to lead them to the picnic. She agrees.

The path ends at a glen set up as a picnic blending 19th-century American and medieval English aesthetics. Pollyanna heads to the pie tent, and a barefoot Tom Sawyer approaches the boys and expresses his enthusiasm for treasure hunting. Billy then spots the Sheriff of Nottingham on a raised platform. The three musketeers and D’Artagnan serve as his deputies, a crossover Tom notes doesn’t match the books. The boys hide behind an oak tree and overhear the Sheriff instruct the musketeers to identify Robin Hood among the archers. Billy spots Hercules, who is thinly disguised in a monk’s robe. Borrowing Tom’s straw hat as cover, Billy heads across the clearing to warn Hercules as the archery contest begins.