The trackers (AUDIO: Movers) were a group of four faceless posthumans who were created by the Blood Coteries and were covered in time-active memeodermic tattoos that allowed them to track members of Faction Paradox.
The trackers' existence intentionally violated the Laws of the Great Houses and they were arrested and taken to the Houses' prison planet. At the time of Demetra Kine's organised breakout, Kine had Selvynkesh release the trackers to find and kill Shuncucker and Justine. The ensuing battle between the trackers and the Faction members spilled into the Labyrinth and the records library was destroyed. While physically immune to shadow-weapons, the trackers were still memetically vulnerable and Shuncucker used a shadow memetic pick to override Kine's control over them. The trackers then killed Kine and joined Shuncucker in battle against the House Military come to return order to the prison. (AUDIO: A Labyrinth of Histories)
Later, near the time of the Armistice, Huxley came across one of the trackers in a dazed and confused state. The tracker was given to a Shift to use as a physical body. The shift was able to extend the body's psychic field to detect if members of House Military were nearby. (PROSE: A Farewell to Arms)