This is a post-UK broadcast review of Doctor Who: Smile. River Song always warned the Doctor against spoilers, so be sure to watch the episode first. Doctor Who broadcasts on Saturdays at 7:20pm UK time on BBC One, and 9pm EDT on BBC America.

Emojis aren't only the future of language for us doomed Earthlings, but we're also the only poor saps throughout the universe who use them. This is one of many things that the Doctor's ace new companion Bill Potts learns from her intergalactic tutor in Smile, the second installment of series 10 of Doctor Who.

While Nardole (Matt Lucas) is left back at base grumpily guarding the mysterious vault in the bowels of the university and making a brew (NB: for our American readers, that's a cup of tea), Bill (Pearl Mackie) tells the Doctor (Peter Capaldi) that she wants to travel to the future. "Why?" he asks. "I wanna see if it's happy," she says.

The Doctor had made a promise—as Nardole is quick to remind him—not to stray "off-world" and leave the vault unless it's an emergency. But the gravitational pull to take his new sidekick to far-flung parts of the universe is too strong. "Between here and my office—before the kettle even boils—is everything that ever happened, or ever will," he tells the ever-inquisitive Bill.

Tiny robots, dubbed Vardies, that aggressively buzz overhead in inky flocks—briefly bringing to mind Black Mirror's episode Hated in the Nation—direct emojibot droids to dish out mood badges to the Doctor and Bill, who have just arrived in a bright, minimalist city on a distant planet. We've already seen in the opening shots of Smile that Kezzia (Kiran L. Dadlani) and Goodthing's (Mina Anwar) inability to grin and bear it, even in the most unhappy of circumstances, simply doesn't cut it for the Vardies.

The microbots intrusively fit the time-traveling duo with a communication device that uses their nervous systems as hardware. There's no privacy-by-design here, and zero clue about who is slurping the data—in a sly nod to current-day concerns about the level of information many of us are sharing online. "We've just downloaded an upgrade for our ears," the Doctor says. Bill's delighted by the tech until she wonders, "what happens when you're in the loo?" The mood for this unsettling adventure is set: "emojis, wearable communications, we're in the utopia of vacuous teens," the Doctor notes.

But as fertilizer made from human bones rains down on a seemingly tranquil garden, it becomes clear to the spirited pair that if you're unhappy, you die.

Before we get to that, though, there's some lovely interplay and japes between Bill and the Doctor. The almost rhythmic dialogue in the script for Smile, written by Frank Cottrell-Boyce, who penned In the Forest of the Night for series 8 of the sci-fi drama, helps the viewer become better acquainted with Bill, following Mackie's terrific character debut—if not storyline—in The Pilot, this season's opening episode of Doctor Who.

It would seem we may also have a running running joke (geddit?) throughout this series, with Bill reprising the "penguin with his arse on fire" line as, from the safety of the TARDIS, she watches the Doctor run toward danger. It doesn't take her long to follow his path, nonchalantly asking him why he has a Scottish accent. "I'm not Scottish, I'm angry," the Doctor says, before he topically japes that people from Scotland are "all over the place, demanding independence on every planet they land on."

Perhaps the comedy in this episode is deliberate, after all it is called Smile. It certainly has plenty of laugh or cry die moments. But the action is at times a bit flat, relying far too heavily on exposition to propel the plot forward. It's an intriguing yarn, but beyond the bright, beautiful Valencia setting (the Spanish city's stunning Arts and Science Museum was used as the main location for the second installment in this series), the whole thing could easily be transplanted to radio.

During a scene that does work visually, Bill reluctantly snacks on a blue cube of algae that she says smells a bit fishy. The Doctor responds: "I met an emperor made of algae once. He fancied me."

Simon Ridgway/BBC

BBC

BBC

Simon Ridgway/BBC

BBC

Simon Ridgway/BBC

BBC

Simon Ridgway/BBC

Simon Ridgway/BBC

Simon Ridgway/BBC

Simon Ridgway/BBC

Hardy Vardies face factory setting of doom

It slowly dawns on the pair that the city isn't quite the garden of Eden envisaged by the final humans left in the universe, who had hoped to colonize it after sending the Vardies, their emojibots, and then a setup team to the planet first.

"There's a giant smiley abattoir over there, and I'm having this childish impulse to blow it up," the Doctor tells Bill, before they both return to the passive-aggressive emoji droids. But the second part of Smile struggles somewhat. We learn that the Vardies are the walls of the city and the original spaceship that brought them here is sunk into the middle of the colony. Cryogenically frozen humans are suddenly disturbed from their pods by Bill and the Doctor's activities as they head for the engine room to blow the whole thing up. All of which feels like sci-fi by numbers.

A little boy and a dead woman help Bill—who, in classic Who fashion, is separated from the Doctor—to figure out what is really going on. The emojibots were built only to have a positive mental state, so the moment that a natural death occurs, they have no capacity for dealing with grief.

The Doctor rushes to tell the humans, who are tooling up for a fight, that the bots "know when you're too unhappy to live." The skeleton crew was toast because they didn't keep on smiling through the "grief tsunami" as their loved ones were wiped out one-by-one by the Vardies. As the emojibots begin identifying as a species, the Doctor takes the easy way out and hits reset. "He turned it off and on again," Bill jokes.

The perplexed humans are told that the Vardies are the indigenous lifeform on the planet and they must learn to live with them. But it's probably now safe to express a whole range of emotions emojis. The lucky people.

Next week, it looks like the poop emoji might come in useful—given that the Doctor and Bill have missed out on that nice cup of tea and are instead standing on an iced-up river Thames facing down an elephant...