The Nine's prison

The Nine created a prison after leaving the Crucible of Souls wherein he captured a number of the Doctor's companions, including Jamie McCrimmon, Jo Grant, Leela, Romana II, Adric, Charlotte Pollard, Liv Chenka, Helen Sinclair and Bliss. He used River Song to give companions names before he hunted them down and placed them in cells, blocked off by temporal fields. Eventually, Liv, Helen, Charley, Bliss and River escaped with the help of one of the Nine's drone sentries and freed the other companions, leaving the Nine locked in a cell. (AUDIO: Companion Piece)

While locked in the cell, the Nine was apparently ambushed by the Ravenous and eaten; however, this was soon revealed to be a ruse. (AUDIO: The Odds Against)