|Book 6: Agent Wallree and the Emerald Sword|
|Book No.: 6|
Agent Wallree and the Emerald Sword is the sixth book in the series. In the book, the Twilight Helmet and the Emerald Sword are stolen from the Museum by Sir Wallace. He puts on the helmet and unleashes the Ghost Knights, turning New Walrus City into the medieval Olde Walrus Ville. Wallree, Wilson, and Wendy quickly race to the scene. They enter the Castle where Sir Wallace is hiding. They reach a rope bridge, and Wallree and Sir Wallace meet up in the center. In an effort to defeat Sir Wallace, Agent Wallree cuts the bridge and they both plummet into the river below. Wallace's dead body washes up on shore, but Wallree remains a mystery. The book ends as a 'To Be Continued...'.
- This is the first mission that Wallree fails.