There was a robbery in progress and you are one of the early respondents. However, when you arrive, the robbers already left. Fortunately, you saw one of them riding the train, so you need to chase the train to capture that robber.
Drive your car as fast as you can, but try to be careful or there won't be any train to catch for you. Grab as many coins as you can because you can use it later to upgrade your car. This would give you a better chance of chasing down the train. Use the booster to speed up your car, so you can catch up with the train.