Mathfinder: One Knight too Many (advanced addition/subtraction)by MindWare
A trip to the museum turns into a dangerous rescue mission when a secret passageway leads you to a strange land. You are forced to face terrifying creatures, an ancient city under siege and the mystery of One Knight Too Many. This intriguing story is a totally engaging new way to build arithmetic skills. The clever mystery is filled with math problems; solve the equations to work your way along the pathway that runs through the book, bringing you one step closer to solving the riddle at the end!