Secret Decoder Game Book from Melissa & Doug's On-the-Go line is a travel-ready activity book that lets kids play spy and solve mysteries using a built-in rotary decoder wheel and a magic-reveal pen; it contains eighteen activity pages with mazes, word puzzles, seek-and-finds and code-breaking challenges, stores neatly in its tab-close cover, and encourages problem solving, observation, and independent play for kids seven years and older.