Dyan Ardais has already taken the monitor's oath when he is summoned home from Arilinn because his father has just killed his stepmother. The oath binds him not to use his powers to force his will on another. But his father is insane, obviously dangerous to those around him, and totally unwilling to listen to reason.
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Used availability for Marion Zimmer Bradley's Oathbreaker
November 2009 : USA, Canada, UK Kindle edition