Reading and writing stories with science-related themes make it possible for students to develop interest in and capacity for scientific thinking when specialist science and more popular genres converge. Additionally, feminist scholars have called for greater use of creative writing activities in school science to counter students' disengagement in participating in science discourses. However, few studies have been conducted into how students construct meaning as fictional and non-fictional science genres are merged in writing activities. The purpose of this interpretive study was to investigate what happens when a class of fourth-grade children co-creates a publishable eco-mystery--that integrates both fiction and non-fiction--with their teacher. Interpretations are organized around two themes; namely, when genres clash, and scaffolding science learning. The study asserts that the children's engagement and interest in the writing tasks were sustained across genres and that the children demonstrated fluency in their use of canonically accurate knowledge of ecological/biological concepts embedded in the eco-mystery with scaffolding from their teacher. Additional evidence suggests that the children's fluency with scientific registers had more than a short-term effect. (Contains 2 figures and 2 tables.)