Spark, a mechanic who dreams of becoming a Racer, has always wanted to own his own engine. Bolt, who comes into the Starlight Repair Shop to be fixed up, tells him that the old ruins are filled with the roar of engines. Spark sneaks out along with his buddy Meep. They find a worn-out old engine and activate it. After rescuing Otto, the gas station owner, in a traffic accident, Spark's life is changed forever.

Under Flash's tutelage, Spark goes through a dull and gruelling training regime. On learning that Harry is about to take on the Skyracer Trail, anxious Spark rushes to the racetrack that very night, taking his engine and his friend Bellows. The Skyracer Trail is full of dangers to which both Spark and Harry fall victim. With their lives in danger, Spark uses his reversing technique to help both him and Harry to escape unscathed.

Spark makes a string of mistakes in training while trying to move as gracefully as Flash. Flash sends him off to retrieve some old tires. It seems like a simple task, but turns out to be anything but. As Spark traverses steep slopes, he comes to understand the true meaning of gracefulness - to be absolutely focused - and finally grasps the secret of the Sprocket.

After their defeat on the Skyracer Trail, Harry can't stop thinking about Spark. During his training, Harry can't seem to get it together. He comes into town to blow off steam, but all he can think about is Spark, and he feels like a fool. Harry comes to the Starlight Repair Shop. When he sees the real Spark, he thinks that Spark is an illusion. At the same time, he realises that Spark's abilities come from a daily routine of hard training, and achieves a breakthrough.

Hairpin also dreams of becoming a Racer, but she has no confidence in herself. When the eccentric Bolt is looking for rainbows all across Tyretown, Hairpin, being kind-hearted and attentive, realises that he has an oil leak. She follows him, and helps him out of a number of sudden scrapes. Bolt gives Hairpin his engine, and encourages her to follow her dreams, telling her that she is the rainbow that he had been looking for.

The Skyracer Trail Challenge is about to begin, and Harry and Spark are getting ready at the starting line when Hairpin appears. In the course of the challenge, the three Racers overcome various obstacles, making use of their previous training. But just as they reach the finish line, a gust of wind suddenly blows them across the track, and though they are competitors, they choose to work together to complete the challenge.