We use a narrative framework to investigate how mathematics textbook lessons can promote sustained student inquiry. Our analysis of four high school textbook lessons on the SSA congruence property, three of which contain explorations, reveals how explorations can promote problem-solving perseverance by inspiring readers to raise mathematical questions and by keeping these questions open throughout significant portions of the lesson. Furthermore, student curiosity and anticipation can be enhanced through ambiguity. Stark structural differences exist among lessons with explorations, suggesting that explorations are not necessarily supportive of sustained student inquiry. These insights not only enable educators to learn whether and how a lesson encourages inquiry but also support the design of new curricular materials aligned with the goals of reform.