Joanna Selbourne, known as "Kenna" is a "psionic" which is to say that she is capable of telepathy and tele-empathy, and under hypnosis to precognition. She is very different in both appearance and behavior from the rest of Stefan Skellen's hirees. Her job, contrary to the orders which Skellen had received from the Emperor Emhyr var Emreis, was to locate and kill Ciri.
She proved instrumental in the capture Rience's spies, using the "Pieróg method". This method consisted of pouring milk and dusting flour on the target area to enable one to roughly determine the location something invisible, then dispose of it. It was only because of Kenna that Rience was located and the whole operation successful.