In this talk, I shall introduce a new modal logic that is suitable to model complex systems evolving over time in a modular fashion. This logic may be regarded as the result of extending propositional linear temporal logic by a second dimension that allows us to zoom into states and thereby to further refine the specification of events associated with these states. In this sense, our logic may be described as an extended temporal logic that combines features from both point-based temporal logics and modal interval logics. From a more abstract point of view, our logic is best described as a modal logic based on frames that are ordered trees.