Keep Kasim away from the flotation chamber | Chapter VII Memoria Guide

After conversation with Ariarchos, who has given Sadja the dagger pick up stones (three). Throw them into the prince. When Kasim use the magic shield, go to the Ariarchos (click on him) and take from him a tower key. Search the bodies of three men. Sadja will take a sceptor, a belt and a quill. Use the key with the tower door.