Emoji robots! Is Doctor Who jumping on a bandwagon? Well, a little, but the thing about bandwagon's is that they have bands on them, and some bands are great. This is the case with this week's Doctor Who episode: Smile. Settlers from the Earth are using robots to colonize new planets. The robots read emotions and communicate using emojis, the aim being to keep the colonists happy… but something goes wrong and colonists start getting killed.

It's a fairly standard science-fiction premise, drawing on a lot of hallmarks of the genre, however, the story feels fresh. Writer Frank Cottrell-Boyce takes a magnifying glass to the idea of communicating via emotions, shining a sideways spotlight on the idea of emojis. Instead of taking a dismissive attitude to the idea of little yellow faces as a means of communication, he takes it to a logical/illogical extreme. To call the episode reminiscent of Black Mirror would not be unfair. There are a few moments where it feels like the plot takes liberties. Without giving anything away, it's difficult to imagine that no-one would have thought to program a failsafe for the scenario that arises. That said, it's an easy loophole to overlook, because the story structure is solid, and the performances sell it.

Capaldi is in great form, showing Pearl Mackie's Bill her first glimpse of the future. Their relationship develops, and we get to see Bill sussing out more of who the Doctor is. Because she has already had several months to get to know him on Earth, we're spared too many critiques of his personality, and we are only seeing her seeing him in this new context. That of: time-traveling alien. Their personal bond is good, she trusts him, and so we are spared a tired "Companion doesn't trust the Doctor and so does something stupid" plot-line. Instead Bill is a gentle tempering force for the Doctor's reckless streak, and an excellent catalyst to him as an idea machine. Mackie is demonstrating herself to be an engaging companion, and she and Capaldi's chemistry is easy and undeniable. It will be interesting to see how this relationship grows.

A few nods are given to ongoing story threads. Nardole and the Doctor talk briefly about 'The Vault' and a promise the Doctor made to not leave Earth until… something. There is also the name of a spaceship that may be a clue to future events. The colonists' ship's name is an anagram of 'Nowhere'. This may be foreshadow, or it may be coincidence. The story has echoes of classic series stories The Sontaran Experiment and The Face of Evil, with the references to a depleted Earth and colonists fleeing to save the human race. All these accents are decorative and fun. Teasing, but un-distracting.

Stripped to the essentials: Smile is a solid, straightforward romp. Strong premise, effective execution, nothing too challenging thematically, but exciting and distinctly not dull. Looking forward to next week's trip to an old-timey, iced over, River Thames.