Defensive actions in critical infrastructure environments will increasingly require automated agents to manage the complex, dynamic interactions that occur between operators and malicious actors. Characterizing such agent behavior requires the ability to reason about distributed environments where the state of a channel or process depends on the actions of the opposing sides. This paper describes an extension to the Applied π-Calculus for modeling agent behavior in critical infrastructure environments. The utility of the extension is demonstrated via an agent-based attack and defense interaction scenario.