How can a student experience what happens in the mind of a mathematician while solving a problem? In this paper we discuss a theoretical design of an educational script, based on digital interactive storytelling. Parallel to Docter's 'Inside Out', the cognitive functions occurring in problem solving become characters of a story-problem. Students play the corresponding roles, alternatively as Actors or Onlookers. Besides the characters, the story-problem evolves along a sequence of episodes according to the cognitive processes involved. The script aims at developing students' mathematics identity as the community of all of characters, together with their interactions while working.