Taking several clues from GDW's Please Cruise module I would set this game in train that is traveling great distances and making few stops. The player would be armed to the teeth transporting equipment. At least two other armies would also be on the train and armed to the teeth as well. Maybe Khador and a large Rhulic mercenary team.
Now have a Cryx or elven mage hunter assassin take out some key players in each camp. Just have the players try to get to the next few stops with all hell breaking loose between the two camps. Everything should escalate on a timer so players taking to long are faced with worse and worse shit going down. When stuff is going nuts have everything stop for tea, which is very civilized and friendly. This scene is out of the Polar Express related to hot chocolate, I just think it would be funny for everyone to stop for tea, or Christmas day or something. Then at the end of the tea or the clock striking midnight the commanders should be talking to another peacefully. Seconds later the commander kills the other and everything goes crazy gain.