In The King of Attolia, we learned that Eugenides friend Sophos, the heir to the kingdom of Sounis had been kidnapped by rebels and then had disappeared. In A Conspiracy of Kings we find out what happened to him. (Essentially, he manages to jump directly from the frying pan, into the fire, yet manages not to get burned too badly.)

A Conspiracy of Kings opens with Sophos and the magus managing to make contact with Eugenides in Attolia.