The portly man looked North over with a critical eye and smirked. "Hrmm. Friendly or not, you're still a damned dirty spy. Put him in chains boys," the man said with a grunt.
Fearing an end to their journey so early, North and the others went along with the man's demands and North was put in chains and taken to a side-office. After allowing the rest of the group, and indeed the rest of the passengers, to pass through, the portly man returned to the room holding North. The man left the rest of the group out in a waiting room, informing them that the charges for aiding a spy were large, and that he needed them on hand until the truth was determined.
The portly man returned to the interrogation chamber where North was locked up and slammed the door behind him. He nearly spat in North's face as he ranted, "Thought you could slip by, eh? Thought we wouldn't catch on... What kind of fools do you take us for? Here you are, proudly bearing the symbol of Karrnath on your chest, getting off of a train from Aundair, and you think that we'll just go along with your 'student of the magical arts' line?"
"Quite the little story you're telling. I can smell it on you, though. You're part of some Aundarian plot with the Karrnathis to bring us down from the inside. Well, you hunk of junk, you'll have to try harder than that to explain why you're coming through Thaliost," the portly man spouts.
He leans forward and screams in North's face, "Now tell me! Why are you here?! What are your masters sending you through for?! Why shouldn't I lock you up for the rest of time, you dirty mechanical spy?!"
OOC: For clarification, I am assuming that North is still wearing the mark that was built into his plating to signify him as an officer in the Karrnathi war-machine. You did not specify either way, and it helps this plot item. It might work in your advantage while you're in Karrnath, but right now you're in Thrane.