From Edgar Award Winner Dori Hillestad Butler comes The Treasure Troop, a chapter book mystery series! Join Marly, Sai, and Isla, three code-cracking kids on the hunt for an old neighbor's hidden treasure.

In the fourth and final book of this code-busting series, Marly, Sai, and Isla are back on the hunt. After their shocking discoveries on Summer Island, the Treasure Troop has one final set of clues to follow before reaching the end of their search. And now our trio must solve the toughest mystery of all: what really happened to Mr. Summerling?