The plot has two parallel stories. Sam has flashbacks that tell how he grew up and ended up with Clarence. It takes talent to make both stories interesting. So often I'll lose interest in one storyline versus the other. You'd think a plot string following a cat would be a dud but the author has some of the funniest parts here. Sam landing on a chihuahua was a favorite. The cat dame he falls for might go over the head of some younger readers, but it echoes the voice of Dashiell Hammett's Sam Spade and had me snorting. He does a terrific job imitating the hard-boiled detective with cat humor.
Most of the story was unpredictable such as the subplot with the goofy hat lady and Sam's adventures, but the judge at the end was a bit obvious. The subplots misleading the reader as to who the culprits are might be confusing for some readers. The author has the jewel heist, an elopement, and corrupt authority taking illegal actions. The more complex the mystery the more I like it, but it might be hard for young readers. Just something to keep in mind.
While most of the action takes place on the train, the climax occurs at the Blue Streak roller coaster at Conneaut Lake Park. I couldn't decide if I thought it was a let down or not. I was less interested in it but that might have been because I had figured out they mystery. I am not sure young readers will feel the same. I think they'll like the whole roller coaster death ride. The epilogue was a nice touch. Don't miss the outrageous Lantern Sam and his nine-plus lives.