This paper presents a novel approach to design and develop an assembly and execution shell for multiagent applications based on the concept of a mission. A mission is a live evolving object that contains data, current variables, goals and evolution history of the mission itself. By maintaining the states and data inside the mission, it is possible to suspend the multiagent system's mission execution temporarily and resume when permitted. Our design allows run-time and dynamic agent generation depending on the complexity of the mission itself. We discuss the design and internal structure of the mission, the strategy and efficiency of the system in executing the tasks in the mission, and present our prototype system called eHermes.