Gisella was in charge of the underwater research base on Flydon Maxima. She looked like a twelve-year-old child with black eyes and dark bobbed hair. She was a mystery, one of a kind. The fact that she never aged was attributed to a rare medical condition termed Adulecentia Perpetus.
When her father, Varlos, a former Brother of the Darksmith Collective, left the Darksmith world Karagula, he took her with him, hiding her away for safety on Flydon Maxima. Following the Tenth Doctor's arrival, she accepted his invitation to help him find Varlos and left the research base to join the Doctor. (PROSE: The Depths of Despair) She found her father in Paris, where he died. (PROSE: Vampire of Paris) She was later revealed to be an android. (PROSE: The Pictures of Emptiness)