The best "Doctor Who" episode in a long time - perhaps since the "Girl Who Waited". First of all, it affected me on an emotional level - it made me cry. But it's also refreshingly otherworldly: we need episodes like this more often, to remind us that the Doctor is an alien, and that he is just as comfortable in alien worlds around thousands of other alien races as he is around humans. There is a wonderful intro on Earth, filling us in on Clara's past, beautiful bonding moments between Clara and the Queen of Years, intelligent dialogue about the uniqueness of each existence and the infinity of possibilities, and of course a speech that must rank as one of Matt Smith's most defining moments as the Doctor. I am a fan of Steven Moffat, but how this episode (which was written by Neil Cross) can have a lower IMDb rating than Moffat's comparatively mundane "The Bells of Saint John" is beyond me. *** out of 4.