I think this has been discussed before in the d-list, just bringing it up again.
Now that we know which unit is fighting who in battle and being able to know who capture who, nobles should be able to keep another prisoner in their own prison. Of course, the judge's prison should be vastly superior in being able to keep a prisoner than a regular knight's cage(or possibly estate if your nice). Anyone should be able to capture a noble and ransom them. However at lower levels your restricted in the ability to do things. So,
Knight's Prison: High escape chance, only action is to release prisoners
Lord's Prison: Medium escape chance due to having better funds for a dungeon. Should be able to take noble's gold and items.
Duke's prison: Low escape chance, but have the same amount of actions as a lord
Judge's Prison: Lowest escape chance. Of course, all actions are available.
I think you should also be able to transfer a prisoner to another person. So if want to say torture a noble, you'd have to send them to the judge in order to get that done. During this transit time, they would have a higher chance than regular to escape.
This will be more realistic in that everyone has a chance of capturing and possibly making some money ransoming nobles.
Thoughts?