heres my idea for a synopsis...
The Doctor and Martha escape in the Tardis after a battle with The Master. The Doctor, badly injured, sets his controls for christmas 2008, but faints and makes it 1666, the great fire of London. As The Doctor begins to go through his regenerative cycle, Martha is thrown out the Tardis to explore this old London town of centuries ago.
Martha is then found by Charles II and is brought to his court and asked to help the people defeat this mysterious force. While at this time, The Doctor, while not yet regenerated fully, has gained some strength and left the Tardis.
Charles II tells Martha of great beasts that roar in the night, breathing out air of poison and flames of torture. These beasts have plans to destroy the world with their power of fire. Can Martha help save the king and the world? will The Doctor help save the day before his regeneration happens? and finally why is there a tingling down Marthas spine that feels like the opposite to the Time Lord she travels with?
i know its a bit crap, but what do you think, it could be possible, and we see the regeneration right at the end of the episode. it would be good, seeing The Doctor go through so much before he goes through change.