Interactive fiction and adventure video games are narrative genres which provide the player with the option of acting as the main character of the story. However these genres do not fully match the expectations of their authors and readers because the player cannot deeply affect the storyline.This article describes a system integrating highly interactive narrative structures in a real-time 3D environment.Based on a theoretical foundation of narrative and drama, an interactive drama engine (IDE) has been implemented. It comprises an action calculus system, a text-generation system, a behavior engine, an animation engine as well as an innovative adaptive user interface. The IDE is demonstrated with two scenarios.