This is an example of a story synopsis. This is the first thing which should be submitted to the script editor.
The Last Colony – by Robin-Mary Manseth
Against the vehement protests of Landon, the Doctor embarks on an illegal plan. He wants to find out what happened to the last known colony of humans before their extinction. This information, however, was deemed forbidden by Rassilon himself. The Doctor, however, insists on finding out.
When the Matrix on Gallifrey does not have the answer, he sets course for Volox, the site of the last human colony. There, he and his companions find a dying sun and a band of human survivors preparing for Harvest: The time when predatory creatures make their final attack. And the humans are ill-prepared.
The Doctor agrees to help. Evading attempts by the Time Lords to stop him, the Doctor finds that even time itself will erase the Doctor and his companions to keep the time line intact. But the Doctor, and even Landon when convinced that the Time Lords should not be able to decide who lives and who dies for the sake of keeping “history” intact, press on. All is not well, though. A traitor is in their midst who sold out the humans for their own survival and time is winning.
As you can see, it is not necessary to have an “ending” at this point. Your conclusion will come in the next stage of the writing process: the rough draft.