[Lady Fiona arranges with the Sluagh for them to destroy the faerie souls of the members of House Leanhaun. The Sluagh agree to do this and swear an Oath of the Long Road on it (the Sidhe are, after all, the rulers of the Dreaming, and Lady Fiona hides the reason for her hatred of Lord Leanhaun behind the need for justice for the slaying of House Balor.
The Sluagh use the iron knives they received from Nocker to destroy the faerie souls, but realise when they are part way through that this has caused them to break their Oath of Guardianship. They go to the Sidhe and beg that they be freed of their Oath of the Long Road, so as not to cause further damage. But the Sidhe refuse, and so the Sluagh refuse to continue the killings, thus breaking that Oath as well. They also go to the Trolls and ask them to free them from the Oath, but the Trolls say that they are unable to, for the Mountain King is dead. [So first we have them unable to do this because the Mountain King is gone, and then later because the Emerald is gone. Good stuff.]
Meanwhile House Leanhaun has had its leader destroyed, and so it doesn't really count as a proper house any more. What happens to those that are left? If they are killed, do their souls ever get reincarnated?]