"I could order the merchants to look for a stranger among their servants. But I don't trust money-bags traders

"I could order the merchants to look for a stranger among their servants. But I don't trust money-bags traders. I'd rather charge my people with watching the merchants. Then again, why look for clues when the best proof is evidence by confession? If you bring me the merchants for a couple of hours, the problem will be solved! The rack will make the spy sing like a bird."