A rogue planet was home to a level 4 society known as the Quiet Ones.

The Quiet Ones had developed technology that captured starlight to power their city. The planet was later caught in the gravity of a pulsar. In order to survive, the Quiet Ones used their technology to turn themselves into pure energy. The Fifth Galactic Surveyor Corps built a base to study this society, and initially assumed they had vanished. The temporal field around the base meant that while minutes passed on the surface, years passed inside. The Second Doctor created a truce between the human surveyors and the Quiet Ones to continue their studies to learn about and communicate with the Quiet Ones, if they did it more quietly. (AUDIO: Shadow of Death)

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