Moriarty's plot to earn one billion (little pinky) dollars is currency speculation. She buys a lot of currency from the Republic of Macedonia, which will (fictionally) soon enter the European Union, rendering its currency "worthless". By arranging an assassination she hopes to turn the tide of a referendum.
This is utter and complete rubbish. First, the European Union and the Eurozone are not the same, but this is a minor fillip--- it is unlikely the EU would admit new members not willing to adopt the Euro. Estonia, for example, had a seven year gap between the two memberships, so it is worth being mindful of the difference.
More importantly, the economics are all wrong. If anything, the foreign exchange value of the Macedonian denar would almost certainly fall if its conversion to the Euro failed. Countries which have joined the Eurozone--- like Slovenia, Cyprus, Malta, Slovakia, and Estonia--- exchange their currency for the euro, they don't just burn all the old currency and start over with empty bank accounts! You can go to the EU's web page and read the changeover plan: for a period of two weeks after "€-day" the two currencies are used in parallel! Banks can't even charge a fee to convert between the two at the official rate!