Doctor Who: Season 10, Episode 2

10 - 2: Smile

In the far future, at the edge of the galaxy, there is a gleaming, perfect city. This brand new human settlement is said to hold the secret of human happiness - but the only smiles the Doctor and Bill can find are on a pile of grinning skulls.
Something is alive in the walls, and the emojibots are watching from the shadows, as the Doctor and Bill trying to unravel a terrifying mystery...