The next ingredient that Philippa needs to heal Saskia is the blood of royalty. For this task, Prince Stennis will do just fine. Explore the series of tunnels forming the town hall to find Stennis. Ask him to provide you with a droplet of his blood. Perhaps understandably, he will refuse. Elaborating upon the situation will yield no further results, however, and this casts a cloud of suspicion over the Prince. Even with Saskia’s life on the line, he refuses to contribute his blood to the potion.
For now, this is as far as you can go in this quest line.
Head outside of the town hall to find a group of pedestrians in a scuffle over Saskia’s poisoning. A few suspects have been named, but no concrete evidence has been found at the moment. Talk to the humans in the center of the rabble to learn of a suspect who has been taken prisoner. He may have some leads on how Saskia was poisoned.
You will find the suspect in the middle of the clearing at the end of town, being guarded by a group of Scoia’tael. Although he will be unwilling to talk at first, using Axii will loosen his lips significantly and you will learn of a conversation he overheard between Prince Stennis and Olcan, the priest who was killed earlier. He will suggest searching Olcan’s home for clues.
Talk to Cecil to mark Olcan’s house on your mini map. It is located on the same side of town where you purchased the traps and grapeshot bombs, but across the way from the merchant’s quarters. Search his room to find the schematics for a goblet. This is all that you will be able to discover at the moment.
In order to progress more with either of these quests, you will first need to uncover a few others. Solve the mystery of the Suspect Thorak quest in order to get the experience points for completing The Walls Have Ears. Meanwhile, you should complete the first segment of the quest Where Is Triss Merigold? (this is an older quest, but it has been recently updated) to unlock further progress in the Royal Blood quest line.