Ok, here is a sample possible scene. I don't claim that its perfect, just a suggested way to approach it. I've tried to listen to constructive criticism of the previous writings.
This scene takes place during Episode 7 . The Battle of Tewkesbury has just ended and the leading Lancastrians have fled from the rout into Tewkesbury Abbey for sanctuary. The Doctor, disguised as a priest, is attempting to help them escape.
NB: Since we don't know the companion will be, I'm using Donna Noble.
Queen Margaret: Verily the Yorkists approach. But we will be safe in here. Even Edward of York would not dare slay us on consecrated ground.
Prince Edward of Lancaster: One is not so sure of that mother. Oh that this too too solid flesh would melt, thaw and resolve itself into a dew.
Donna *to the Doctor*: Are they really safe in here Doctor?The Doctor Of course not. Don't you know your history Donna? The Lancastrians start to get massacred in here. However the chroniclers record that a priest intervenes and stops the bloodshed. And I shall be that priest!
Suddenly there is a loud crash as the door is smashed in and the Yorkists rush through led by King Edward IV along with his brothers the Dukes of Clarence & Gloucester.
*a fanfare of trumpets*
King Edward: Now is the summer of our discontent! Raise thy swords and halberds high men. The enemy is ours!
Clarence: Lets waste 'em!
The yorkists begin to massacre the Lancastrians , however the Doctor jumps in between them, holding up his silver cross.
The Doctor: In the name of God stop this now! You are defiling consecrated ground. I realiase that the concept of a war crime hasn't been invented yet, however this is the age of chivalry. And mass slaughter in a church is lowbrow and unworthy of knights.
King Edward: He's right men. STOP!
They stop the massacre. However as they leave the abbey church, Edward gestures to Gloucester:
King Edward: Richard, bring the boy outside with us!
Gloucester grabs Prince Edward of Lancaster round the neck & frogmarches him outside.
Donna: Doctor do something, they'll kill the boy.
The Doctor: Sadly they do. And we cannot change history.
Donna: But you can save him without changing things. Just do a deal whereby you promise to take him to the future in the TARDIS and everyone just pretends he's dead.
The Doctor: Good thinking Donna.
They run outside where King Edward is interrogating the Prince:
King Edward: Verily, why did you come here?
Prince Edward of Lancaster: Because you usurped my father you fatfaced ****.
The King slaps him round the face with his armour glove.
King Edward: Foul mouthed urchin.
Clarence & Gloucester draw their swords however the Doctor intervenes:
The Doctor: Look there has been enough bloodshed today. Let us resolve this peacefully and calmly. Violence begets violence. Surrender the Prince to me and I promise that he'll never threaten you again.
Gloucester: You must think we're thick as a knave.
Clarence: *punching the Doctor* Keep out of it.
Donna: screams as they run Prince Edward through with their swords.
Prince Edward of Lancaster: Out, out brief candle........... *dies*