The Twilight Helmet is the magical helmet that gives the wearer total control over the Ghost Knights, which Sir Wallace did. He stole it from the Museum. The Twilight Helmet was lost when Sir Wallace and Agent Wallree plummeted into the river in Agent Wallree and the Emerald Sword. Wendy and Wilson found the Emerald Sword after the two fell, but the Twilight Helmet is thought to be lost forever.