Shift Agents were entities without solid bodies. They could transfer their energy into mechanical objects and control them. When a case of dark matter came to Earth in 1885, a Shift Agent came to Earth to retrieve it. It possessed a steam train, as it was the fastest transport at the time, and moved at dangerous speeds to reach Euston station faster. The Eleventh Doctor, unaware of this, stopped the train. When he learned the truth, he helped the Shift Agent reach Euston station, where it safely disposed of the dark matter before it did any serious damage. (COMIC: Track Attack)