If someone is accused (or straight-up guilty) of a dishonorable act...

In what situations would the knight (or the lady's champion) be able to avoid losing Honor by challenging anyone who spoke ill of him or her? When would he be unable to do this?

First and foremost by narrative (GM) fiat. If it fits the tale it should be allowed. :D
Other than that it is up to the liege who is ruling the accusation. So depending on the liege's just/arbitrary he can allow/disallow a Trial by Combat.

If you want to get technical the during the anarchy period it should be OK to always claim Trial by Combat and get away with most that way. When Arthur's law comes into effect it should only be available when its word-against-word. So that if there are several equal winesses or a higher ranking witness you could never claim it. Remember that the rank of witnesses are really important.

Note that a villain could use the reverse of this against the PK. First by accusing the PK of X, then when the PK claims Trial by combat, the villain regretfully declines to do battle and withdraws the accusation "well it was just a rumor never mind". That way the accusation was never tried in court and thus the PK was never "cleared" before his peers. ;)
Sort of like a lawyer making a statement knowing an objection will delete it from the record but just having said it might affect the jury.


Also if one of my PKs would knowingly defend what is "wrong" in a Trial by Combat, then I force a fumbled passion roll on them. >:(


Oh and here is the mallory passage of the traitorous queen if it helps you.
http://www.sacred-texts.com/neu/mart/mart460.htm

Also if one of my PKs would knowingly defend what is "wrong" in a Trial by Combat, then I force a fumbled passion roll on them. >:(

I'd be careful there. Auto-fumbles amount to Bolts Of Divine Retribution from the GM and are generally not how Passions are meant to be used. Demanding a passion roll if their honor is above 15 is far more appropriate. And remember that a knight can justify anything to themselves (particularly if they're Arbitrary in the Uther/Anarchy period), so the best way to do this is to wait for a contradiction before second-guessing them.


Oh and here is the mallory passage of the traitorous queen if it helps you.
http://www.sacred-texts.com/neu/mart/mart460.htm


Thanky.

I'm with Ramidel. Did you mean you automatically cause a fumble?

One thing the rules do allow you to do is inflict shock (roll 1d6 on the statistic loss table) when a passion causes you shock. You are free to apply that whenever you think it's justified - but still, it should only apply when the passion is being 'hurt'. For instance, when the lover you have an amor for unambiguously spurns you and tells you she never wants to see you again.

The times I've used it, I've asked players to make a passion roll. Sometimes, I'd only apply this to those with 16+ passions. If they succeed, they suffer the shock (and gain an experience check!); if they fail, they don't suffer shock, but lose a point in the passion - they obviously don't care enough to suffer shock

Technically, shock means you fail to accomplish an action you're Inspired to complete. Fumbling a Passion roll means you go mad and run off into the woods.

That's only the most common situation for which you suffer Shock. From page 73 of KAP 5, note the 2nd paragraph:

Shock: If a knight should somehow fail to perform a
deed for which he was inspired, he suffers shock. In game
terms, the character must immediately make a roll on Table
5–2: Aging.
Note: The Gamemaster may impose shock on char-
acters (with or without their first being inspired) in other
appropriate situations as well. Likely circumstances for im-
posing such a state might be after the knight has just aban-
doned a lord or a lover to grave danger or a dire fate.

I have to disagree with Spoonist on several points here:

First off, I'd be a bit more free with Trial by Combat. Technically, it was a right of a knight, and a Noble who ignores that right is asking for trouble. He's basically denying someone thier rank, and treating them as a commoner. It will set a very bad precedent, unless the Noble can come up with a good reason to refuse it.

I also disagree about "Arthur's Law". Outside of T.H. White and the film Camelot, Arthurian literature does not support the view of law superseding trial by combat, and even Camelot had Lancelot fighting off those who accused him of adultery with the Queen.

I disagree about a villian using trial by combat to slander someone, too. Withdrawing an accusation means that the change is not valid and the accused is considered innocent. Accusing someone and then declining to back it up would cause more harm to the accuser. He would either be considered a coward for not backing up his accusation, or a lying scoundrel for attempting to besmirch a knight's honor on "just a rumor". When a knight accuses someone he is making a statement that what he says is the truth (at least to the best of the accuser's knowledge).

As for forcing a fumbled passion roll on a PK for knowingly defending "what is wrong", I find that ridiculously and heavy handed. I'd also question why the NPCs are immune from automatic insanity in such circumstances?