Donna: 'You fought it off with a water pistol! I bloody love you!'At the heart of tonight's episode was a question which has plagued the fictional time traveller since time immemorial: is it permissible to risk the future in order to save the past? For the Doctor, an old hand at these sorts of conundrums, the answer was a resounding no. For Donna, a relative newcomer to wide-scale catastrophe, the question raised all manner of complex considerations, and provided a stark introduction to the moral quagmire of time tourism.
