In high school geometry courses, students are often given a prepackaged statement that they are asked to prove. In these situations, the process of writing proofs is being abridged, if not misrepresented. To provide her students with a more authentic experience in writing a proof, the author provided them with a summative project for which they had the opportunity to explore a problem, make a conjecture, and then write a proof to justify that conjecture. In particular, the assignment examined in this article, the octagon problem, was developed from a piece of children's literature. The octagon problem is a rich mathematical task requiring deductive reasoning that incorporates several geometric concepts. After discussing how the project was conceived, the author provides the details of the assignment and information about her students' prior experiences in geometry. For the remainder of the article, the author shares the students' work and the challenges encountered with writing the proof. (Contains 10 figures.)