In the Storyline approach a fictive world is created in the classroom. Learners become characters in a story, which develops as they work in small groups on open key questions, devised by the teacher on the basis of curriculum content and in which practical and theoretical tasks are integrated. Though established in first language contexts, Storyline is less known in second language education, although it would seem to offer conditions considered to promote language development in young learners: the story framework provides an engaging and meaningful context in which learners use their language skills holistically, in tasks which simulate the way they might use English in the real world, and in which they can use their creative talents. This multi-strategy case study investigated the language development of a class of Swedish 11-13 year olds who took part in Storyline, Our Sustainable Street, lasting five weeks. In the topic the learners were families living in a new street in a fictive English town. The aim was to consolidate their existing structural and lexical knowledge, develop their language skills and introduce the lexis of sustainability. Findings show that the learners became engaged when they worked with the Storyline, and that this impacted positively on their language development, especially regarding the learning of new words, losing the fear of speaking English before their peers, and in the voluntary production of longer and more structurally and lexically complex written texts. Features which contributed most to learner engagement were found to be group work, art work and the variety of task types, with the boys also motivated by not working with a textbook and girls by opportunities to use their imagination. The results suggest that inclusion of the Storyline approach in a teaching repertoire can facilitate language development in young learners.