At the end of a standby shift the ground crew had just finished plugging the aircraft with intake plugs, pitot covers and prop stops. The pilot was inside the cabin when the ramp manager approached with a dispatch to a fire. The pilot stayed inside the plane as the mechanic unplugged the aircraft. The pilot watched as the mechanic traveled around the airplane grabbing the plugs and other equipment and placed the items into the plane. As the pilot began to start the right engine the ATS (Air Tactical Supervisor) yelled “stop engine” and the ramp manager was giving the stop engine sign. After aborting the engine start they discovered an engine plug still in the right engine intake. Even thought there was no damage to the engine there are several lessons to be learned from this event: 1. The pilot in command is responsible for the pre-flight of the aircraft. It would have only taken a few moments to perform the task and ensure a proper preflight. The pilot described this as “a classic example of “complacency.” 2. The use of ramp managers and other personnel are invaluable to the safety of the aircraft and the aircrews. This situation shouts CRM. In this case the ATS was watching the ramp manager as the pilot was looking at the flight panel. Using the two-crew members in the ASM role caught the engine stop signal way before the pilot would have if it had been a single pilot operation.