While at summer camp, Domingo and Carmen Rivera are excited for the big Camp Rivals Race, an annual cross-country running competition. But during the boy's race, one runner trips and knocks over several competitors. Then another runner interferes with Domingo and keeps him from finishing in a higher spot. What's going on? Are the boys conspiring against Domingo and the other runners from his camp? And what will happen to Carmen and the girls during their race? Follow Domingo and Carmen as they track down the clues to reveal the truth about the rival runners' plans in this exciting sport mystery!