The Boundless by Kenneth Oppel

Will is traveling across the continent on the first railroad tracks through the mountains. The train is miles long and is carrying the dead body of the former owner of the company. This railroad car is electrified to protect the body and some other secret treasures, including a golden spike worth thousands of dollars. There are only two keys into the car; Will's father has one and the guard has the other. Will manages to get his hands on a key after he witnesses the guard's murder, but the killer is now after Will. Will gets help from the owner of a circus traveling on the train, but there aren't many places to hide. He discovers the murderer has other helpers on the train, and they're getting closer to finding Will. To make matters worse, he finds there are other dangers that may worse than this killer!

 Most of the story reads like an adventure, but there are elements of fantasy. A Sasquatch is introduced early in the plot, and it reappears later in the book. The circus owner is a magician, and he's trying to find a painting with the power to save his life. There are also supernatural moments with time and a deadly hag. The story's setting created suspense, because Will was forced to stay on the train knowing that killers were nearby. The circus acts added some entertaining moments and helped save Will's life several times.