Scenario-based specifications such as Message Sequence Charts (MSCs) are becoming increasingly popular as part of a requirements specification. Scenarios describe how system components, the environment and users work concurrently and interact in order to provide system level functionality. Each scenario is a partial story which, when combined with other scenarios, should conform to provide a complete system description. However, although it is possible to build a set of components such that each component behaves in accordance with the set of scenarios, their composition may not provide the required system behaviour. Implied scenarios may appear as a result of unexpected component interaction. In this paper, we present an algorithm that builds a labelled transition system (LTS) behaviour model that describes the closest possible implementation for a specification based on basic and high-level MSCs. We also present a technique for detecting and providing feedback on the existence of im...