The Doctor & Martha discover a planet under a threat they do not deserve.
Graveyards Of Travyard
Prologue
That night, on Travyard, hell was let loose.
The peaceful race of the Grittets was shaken. They had limited technology, and, if they were Earthlings, would fall under the "critically endangered" category. And that was before the disaster.
They were mesmerised by that light. Just that brilliant blue light. That's all it took.
Once half of the species arrived there, that was it. Those who found the light had found death.
That night signalled the death of half a species.