Everything you need to understand or teach Murder Against the Grain by Emma Lathen.
This novel provides an interesting variation on the theme of greed, which is ubiquitous in the series. Given that several of the suspects are Wall Street bankers or brokers quite wealthy in their own right, Thatcher is puzzled as to why they would jeopardize their vested interests for such a relatively small sum of money. One of the explanations advanced is the "New Life" theory. Even a wealthy man might steal such a sum of money simply to be able to disappear and begin life anew in a country from which he could not be extradited.