Melody Bird has discovered an old, abandoned building on the edge of town....

It's a dark, creepy place, but she can't resist its pull. When she goes to explore, she finds a boy hiding out there.

Hal tells Melody that he is a spy-in-training, using the house as a base for his undercover surveillance of a nearby suspected criminal. He's very secretive about the details, but Melody trusts him and starts bringing him blankets and sneaking him food. She confides in her friends Matthew and Jake about Hal - they immediately question the likelihood of a 12-year-old spy and decide to turn the tables and spy on him, to work out what he's really up to....