You must make a self-control roll any time the GM feels you show an unreasonable degree of caution. If you fail, you must go ahead as though you were able to handle the situation!
You may fight – you may even start fights – but you may only use deadly force on a foe that is attempting to do you serious harm. Capture is not “serious harm” unless you are already under penalty of death or have a Code of Honor that would require suicide if captured. You never intentionally do anything that causes, or even threatens to cause, injury to the uninvolved – particularly if they are “ordinary folks.”
You may fight – you may even start fights – but you may never do anything that seems likely to kill another. This includes abandoning a wounded foe to die “on his own”! You must do your best to keep your companions from killing, too. If you do kill someone (or feel responsible for a death), you immediately suffer a nervous breakdown. Roll 3d and be totally morose and useless for that many days. During this time, you must make a Will roll to offer any sort of violence toward anyone, for any reason.
