The captain is Hotah, and he's looking after Prince Doran Martell, the man in charge of Dorne who couldn't go to visit Tywin himself because he is full of gout. But at least he's staying a nice seaside resort.
The prince's brother Oberyn was killed fighting GREGOR, and his three daughters visit Doran with various plans. One daughter wants to declare war on Tywin and destroy, for some reason I don't understand, Oldtown. Another daughter would be content with a few assassinations. Jaime, Cersei, Tywin and Joffrey. Well, half her work is already done. The third daughter wants to declare Myrcella the Queen of Westeros and then just slaughter Tywin's armies when they attack in retaliation to that, Dorne being one of those really very defensible places that no-one has ever conquered.
So Doran travels to the city of Sunspear, where it seems the people are baying for Lannister blood because Oberyn was popular. It seems like he has to choose which daughter's plan is the best, but instead he orders Hotah to lock all three of them (and their families) up, and stay loyal to Tywin. Boy, is he in for a surprise.
