As they get there - they see the tower of the Cloud Ray's where the templars - the brides - keep their steeds.
She will offer them a choice of bodies for their dark mark to migrate into once she has killed them. A line of women in templar uniform are brought in. They are told to choose one.
After they have chosen one - she will kill them and their mark will crawl across the floor and up the body of their chosen woman. They become them. If they try and escape - the templars will come after them. They can try and get to the Cloud Ray tower and escape.
If they choose a body then Siemhouk will ask them to kill Arru at the Temple of War she has betrayed us to the Dead Snakes and Nibenay your husband the king wants her dead. She does not have the mark that you bear - you are shadow brides - she does not even know of your existence. Kill her and return here to prove your loyalty to the king.
In reality Siemhouk has framed Arru as she is really the member of the Dead Snakes. She says this if the players fight her - she says that Siemhouk has set her up. But she doesn't know why or about the Dead Snakes.
The giants and others at the temple will not intervene in a fight between templars without knowing the wishes of the king.
If they come back they will be told to travel with the other The Shadow Brides of Nibenay to destroy Salt View the secret slave city the players have been supporting.