John stopped the guards from attacking, but he asked them to keep the ethereal at a safe distance. Wease had the assassin class. He might have used the class' speed and the invisibility from Vanish to sneak here.
John didn't think the enemy send only one person to take out their command post. He had a few scouts near the command post make another sweep to check if there were other enemies nearby.
As for the lone ethereal, John called out to him, "You have half a minute to deliver the message. After that, you will be executed."
Wease seemed to be fully aware of his possible demise. He was wearing an amulet of rebirth on him.
"Here," Wease took something out. It was a circular plate.
"What is that? Is it a bomb?" John asked.
"Does it look like a bomb?" Wease asked back.
"I don't know. Does everything look like anything in this frigging game world?"