Ellen had spent three days searching for the sticky note.

Ellen had torn through the obvious spots: the desk drawer, the kitchen junk drawer, the corkboard by the phone. Nothing. She’d checked the refrigerator (too predictable), the bathroom cabinet (too damp), even the underside of the computer mouse (her grandmother’s old trick). Nothing.

Her grandmother, a retired cryptographer with a flair for the dramatic, had left no will. Instead, she’d left a trail of sticky notes. Dozens of them. Under the teapot. Inside a winter boot. Taped to the back of the bathroom mirror. Each one led to another, a paper chain of riddles spanning the small, dusty house.

Ellen unfolded it with trembling fingers. “The key is behind the thing that never moves.”

Where are sticky notes stored?