Welcome Back To Chestnut Close, Whose Residents May Not Always Be Exactly Who They Seem... Clever, Curious Melody Bird Has Discovered An Old Abandoned House In The Corner Of The Graveyard, And A Mysterious Boy Hiding There. Hal Tells Her That He's A Spy-in-training Using The House As A Base For His Undercover Surveillance Of A Known Local Criminal. Her Friends Matthew And Jake Don't Believe That A Twelve Year Old Would Be Entrusted With This Mission And Turn The Tables To Spy On Him, Uncovering Secrets And Unravelling A Mystery As They Go.