The cambist, who is in charge of the currency exchange for the country, attracts the attention of a bored and dissolute nobleman, who attempts to trick him, but soon gets caught up in the notion that all transactions and economics is based on the exchange rate of one kind of thing to another. I don't really like economics, but this story was great. It broke down the ideas behind "value" and "wealth" in a way that both made sense, and kept my interest, and although it's a longish story, it's plotted in such a way that my attention never wandered and I never got impatient.