A high fidelity testbed for large-scale system analysis requires emulation to represent the execution of critical software, and simulation to model an extensive ensemble of background computation and communication. We leverage prior work showing that large numbers of virtual environments may be emulated on a single host, and that the time stamped interactions between them can be mapped to virtual time, and we leverage existing work on simulation of large-scale communication networks. The present paper brings these concepts together, marrying the scale emulation framework OpenVZ (modified earlier to operate in virtual time) with a scalable network simulator S3F. Our algorithmic contributions lay in the design and management of virtual time as it transitions from emulation, to simulation, and back. In particular, inescapable uncertainties in emulation behavior force us to explicitly set and reset timestamps so as to avoid either emulator or simulator having to deal with a packet arriving in its logical past. We provide analytic bounds and empirical evidence that the error introduced in resetting timestamps is small. Finally, we present a case-study using this capability, of a cyber-attack with the smart power grid communication infrastructure.