Mystery Train

Mystery Train Island is the 21st island released on Poptropica.

Plot synopsis
Mystery Train Island takes place during the 1893 Chicago World's Fair. Here is the description from Poptropica: How do you solve a mystery when everyone is a suspect? It's 1893, and some of the world's brightest minds are traveling by train to the World's Fair in Chicago. But after a dastardly crime puts the fate of the Fair in peril, only you can piece together the clues and collar the criminal. All aboard for a whodunit that will keep you guessing until the last twist of the tracks!

Sneak Peek
Before it was released, you could play a sneak peek game for Mystery Train Island called "D.C. Diner". It's kind of like Diner Dash. You have to get people the food/drink they ordered, wash their dish and serve the next people in 1 minutes and 30 seconds. Also when someone is done 30 seconds is added to the clock.

Trivia

 * The crook is Mademoisou Mondeau, making the island the 6th (after Super Power Island, with Betty Jetty Reality TV Island, which depends on the last contestant, Counterfeit Island, with the Black Widow, Big Nate Island, with Mrs. Godfrey, and Cryptids Island, with Gretchen Grimlock) to have a female main antagonist.
 * As Counterfeit Island, it a investigation crime island