Scott has kidnapped Mrs. Whitman's dog, Gloria, and is holding her for ransom. But his main motivation is revenge, not money. Mrs. Whitman is Scott's teacher, and she flunked him in math class. Scott's annoyed at this because it means he'll miss out on a hiking trip to Yellowstone National Park and will have to go instead to summer school in order to get a passing grade.

But instead of blaming himself for flunking math, he chooses to blame Mrs. Whitman instead. And so Scott figures that she should pay for flunking him by having something precious taken away from her. It's only later on, in a conversation with his dad, that Scott owns up to his responsibility for failing math class. As he freely admits, he simply didn't study that hard.