It's about a man, who wants power. He would have been ok without it, but his wife convinces him to kill his king so he can then become king. He does that, but then both he and his wife feel guilty about it. And then they become murder suspects. It all ends with a big confrontation.
The point of it is to show that man can be greedy. If he does what he knows is wrong to gain power, he will cause his own downfall. If he hadn't murdered the king, nothing bad would have happened to him most likely.