Almost a Fairy Tale

Once there was a demonic king who had enormous power. He was cruel but his manners were seemly. Thus he could order a regular beheading of five people and they all were almost pleased at the turn of events. On the global scale he was not the worst of course but this knowledge didn't help the people of his kingdom. There were many rebel groups that made plots to overturn him. There were various attempts but none of them was successful. It almost seemed that it was impossible to hurt him. Therefore everyone was surprised when the king was killed by a small peasant boy. He had brought with him a tiny, slimy frog which appeared to be poisonous. Living by the river had made peasants immune to the poison of the frog so noone had any idea that it might kill the king. Oddly enough that was the key to their success because the king had the ring that changed colour when someone nearby had a plan to kill him. The boy had innocently showed the frog to the king, the king had patted it and few moments later had dropped dead. I could say that further on they all lived happily ever after but that would be a lie. They had a horrible  uncertain period  full of riots where one family turned against another while they found a new suitable king. After that the situation improved a bit but even that didn't last long as they were soon conquered by a fierce king from far away and his rule was worse than ever.