The aim of the article is to highlight and explore challenges and possibilities for literacies development within a story-driven transmedia game using mobile technology. Two classes of 7th grade students from two different schools in Sweden participated in the game. During the game, groups of students are supposed to solve a mystery, while being active and finding clues connected to physical places, and to engage in various literacy activities. The participants interpret texts and interactions produced by the game master in the role of different characters within the game. To solve the mystery the participants also have to produce blog texts, photos, films, podcasts and other media. Data from game sessions was collected though participant observations and blog analyses, focusing on signs of engagement and involvement. The study concludes that major drivers for being motivated by transmedia game activities were to be found in the interaction with the game master, collaboration among group participants, number of postings as well as complexity in utterances in written language, pictorial contributions and compositions, entering an imaginary "as if" gaming mode. Hence, transmedia games provide an educational structure that involves the majority of students in their multiliteracy development. The game enables teachers to target those who would benefit from specific multiliteracy guidance while playing to enhance learning. Further transmedia game designs should therefore explicitly incorporate a teacher role in games.