Eustace had originated as the skull of a Fendahl Core and still possessed vestigial life. Glowing with power, it drained life from the Fourth Doctor. Fendelman's employee and the leader of a coven, Maximillian Stael, used it as the centrepiece of a ritual successfully attempting to imbue Thea Ransome with the power of the Fendahl, turning her into another Fendahl Core. The Doctor put it into a lead-lined box and took it into the TARDIS, so he could throw it into the heart of a supernova, in the constellation of Canthares, to destroy it. (TV: Image of the Fendahl)