Your king may accuse you of treason on any grounds he sees fit. A jury of your peers (other nobles of your kingdom, randomly selected) decides your fate. If all vote for conviction, you are put to death. If you do not show up at your Overlords fief for the trial, your fiefs will be seized and your son will not be able to inherit. You are not out of the game, but are a fugitive, subject to execution if caught (which will put you out of the game).