With codewords and secret signals perfected, best friends Rachel and Joon are ready to spend their summer practicing spycraft—especially if they can uncover secrets like the one Joon’s parents have been keeping, that his family is about to move out of town.

When eavesdropping leads them to a ring rumored to have belonged to Anna “Nancy” Smith Strong—according to local Long Island legend, the only female member of George Washington’s famed Culper Spy Ring—they think they’ve hit the jackpot. Then they discover Nancy left a coded message in the ring!

Decoding her message leads to another cryptic clue, and then another, and soon Rachel and Joon are racing to decipher a series of puzzles that must surely lead to hidden treasure! But can they solve the final mystery before Joon’s moving day? And just what did the centuries-old spy hide away—and why?