Toby, an only child, lives with his mother, a single parent. He has a close relationship with his grandparents and especially with Grandy. Looking for something to do during their school holidays, Toby and his friend decide to build a billy cart. With some welcome advice and a little assistance from Grandy, the boys work to overcome many setbacks and impediments and suffer some emotional highs and lows as their cart progresses to completion. During this time, Toby gets to spend weekends with his dad. Together, they share several exciting experiences that stimulate Toby's imagination and determination. Eventually, the cart is completed. However, testing of the new "race car" doesn't go quite as expected. The end result is surprising and quite unimaginable.