Dora and Boots were at a train station to see the trains. Dora and Boots saw a large green train, a medium red train and a little blue train named Azul. The red and green trains had whistles. But Azul, the blue train, did not have a whistle, causing the other trains to make fun of him. Val the Octopus makes an announcement through the speaker saying that there is a big train race. Val the Octopus mentions that the first train to cross the finish line at the big yellow station wins a new whistle. Azul the blue train did not know how to get to the big yellow station. Dora and Boots ask Map for help. He says that they have to go over a big mountain, through a tunnel to get to the big yellow station. Dora and Boots climbed on Azul the blue train. Val the Octopus calls out to all the trains to start their engines. She then said "on your marks..., get set..., go!" and the race was started. Dora and Boots rode on Azul the blue train to the big mountain. Azul tries to trundle his way up the mountain but it was too tall. Dora and Boots gave Azul some encouragement. They cheered for Azul. Dora and Boots cheer for Azul as he trundles his way up the mountain. After that, Dora and Boots get to the tunnel. Dora stops Azul the blue train. Dora told him that it is dark in the tunnel and they will not be able to see where they are going. Dora checks Backpack for something they can use to see in the dark. Backpack had a flashlight which was just the right tool to use to help them see in the dark. Dora and Boots enter the tunnel riding Azul the blue train. Once inside, their voices amplified. Suddenly, they heard another train coming in a different direction on the same track. Dora and Boots had to figure out how to stop the gray train before Azul bumps into him. Azul did not have a whistle. So, Dora asks the viewer to be their lookout. Dora and Boots had to act like a train whistle to get the gray train to stop. They say "choo choo" a couple of times and the gray train stopped just in time. Azul the blue train had to go through the tunnel. So the gray train backs up while Azul went forward through the tunnel. Then, Azul took Dora and Boots out of the tunnel and the gray train switched to a different track and waits in a siding. The gray train wanted to know the reason Azul was going so fast. Azul explains to the gray train that he was in a race to get to the big yellow station and is planning to win a whistle. Azul thanked the gray train for letting him pass and then he had to get going and make it to the big yellow station. Azul the blue train surpasses the red and green trains. Boots tells Dora that nothing can stop them now, not even Swiper. Dora does not know so she decides to ask the viewer to lookout for him. They pass him but then Swiper gets on a pump cart and goes after Dora, Boots and Azul. Swiper changes tracks and overtakes them. Swiper was planning on swiping the train tracks. Azul the blue train stops and Swiper hides the train tracks. Dora and Boots climb out and had to figure out what shape the tracks were and what color they were. The tracks were square and were colored blue. Now, they counted how many train tracks Swiper swiped. There were 5 missing train tracks. Now, Dora and Boots had to figure out where they are. With the viewer's help, they find some blue squares and then they find a blue triangle and a green square. But they managed to find all the squares that were blue. They counted once more to make sure they had 5 blue train tracks that are shaped like squares. After that, each train track gets put back into place one track after another until all the gaps were filled up. Now that all the train tracks are put back into place, Azul carried on with the big train race. Azul was falling behind. The viewer, Dora and Boots cheered for Azul. The cheering was working and Azul went faster. Azul went so fast that he gets to the finish line first at the big yellow station. Azul was proud that he won the big train race. The red and green train were in shock and thought there was a mistake. There was no mistake at all and Val the Octopus announced that the winner was Azul the blue train. Val the Octopus was about to put the new whistle on Azul the blue train when Swiper was nearby. Swiper peeks behind Dora and Boots and jumps off Azul. Swiper was heading for the whistle. Dora, Boots and Val the Octopus stop Swiper by saying "Swiper no Swiping". Swiper gets stopped and runs away. Val puts the new whistle on Azul and gives the whistle a test to see how it works, causing the other trains to accept him.