The Knight and the Lion

"The Knight with the Lion meets Gawain"

By now the castle of Pesme Aventure was far behind. The girl showed the way, and they rode on, never resting, until they came to the house where the Younger Sister of Noire Espine lay recovering from her sickness. It was clear from her face she had been ill a long time, but when she saw Yvain she was full of such joy that she rose at once from her bed and went to greet him.

The next day they set off for the town where King Arthur had been staying for several weeks. They slept that night in a small, poor house, where no one knew them. The Elder Sister too was in the town, staying at the castle. There was only one day left of the forty days - yet the Elder Sister was sure her sister would not turn up to bother her. How could she find anyone to fight Gawain?

Gawain had been away from court for some time - no one but the Elder Sister knew where. On that day he rode into the town wearing armour and carrying weapons so different from his usual ones, that even those who knew him well did not recognize him.

The Elder Sister spoke to the King:

'My lord, it is almost noon. My sister clearly isn't going to come. She hasn't found anyone to fight for her. So I've won, and now I can go and enjoy my lands and castles. She'll never come near me again. Let her be poor and miserable for the rest of her life.'

The King could see that the Elder Sister was unkind and unfair, and he answered her:

'My friend, the King's justice will not be rushed. There's still plenty of time for your sister to appear.'

At that moment, Yvain in his armour, and the Younger Sister with him, rode towards them. The lion had stayed behind this time. The Elder Sister's face turned purple and black as thunder clouds, but the King greeted the Younger Sister with delight.

Yet still the Elder Sister would not give way - even though the younger one was asking only for the half of the land that was hers. She insisted the matter must be decided by a fight, and so the two knights were led out to where the combat was to be. People came running from all sides to see it.

Here knightly combat is being used to decide who is in the right?
How did Medieval justice work?