After defeating The Hissler--and discovering their power as a team--The League of Secret Heroes are ready for their next adventure. When Akiko, Mae, and Josie learn that a spy is betraying secrets to the Japanese military, they join Room Twelve in San Francisco for important work with other code-cracking experts.

But soon there is another very personal code to crack: Akiko is shocked to see her mom walking with the suspected spy, where Akiko's family used to live. San Francisco had been their home until Executive Order No. 9066, which sent Akiko and all Japanese Americans on the West Coast into internment camps.

Akiko fears her mother has become tangled up with something sinister, and soon, more evil forces are menacing the very camp where Akiko's family is supposed to be. With the help of her fellow Secret Heroes, can Akiko solve the most important puzzle of all?