I'm beginning to think that the Doctor is a tragic hero, perhaps this much was obvious to others before, perhaps this is what the viewer is supposed to think, but it was in this episode where I finally clocked it. The Doctor explains how no matter what he or anyone else does to a fixed point in time the outcome is always the same, he later attempts to change history but his own words ring true and he changes only minor details, the bigger picture aka outcome remains the same.
Review of The Waters of Mars
