You start your research. You've already done some reading on the topic in the past and you have an idea of what it's about and where you might want to go with it. In fact, there's a family connection here that you might be able to draw upon. While you're still not sure how you will present your research, you're confident that you will have research to present!
This is actually a good position to be in. The reality is, that we are asking the students to come to an understanding of some area of the curriculum and the project itself is a mechanism for increasing engagement and deepening understanding. The student in this scenario is already engaged in the topic and has some personal connection and past reading that will ensure that he will go deeper than your average student. At this point, the task is to find the vehicle for engaging the rest of the class in his work.