First broadcast 24 April 2010.

The Doctor (Matt Smith) and Amy (Karen Gillan) come to the aid of the Doctor’s mysterious future associate River Song (Alex Kingston). The starship Byzantium has crashed into a long-abandoned stone labyrinth on the planet Alfava Metraxis, and its cargo – a Weeping Angel – has escaped into the maze. Together with a squadron of clerics they head into the labyrinth to catch and disable the Angel before it’s too late.

“The Time of Angels” was the first episode of Doctor Who that Matt Smith and Karen Gillan made, and if you weren’t told that you wouldn’t have guessed it. They leap into their roles seemingly fully-formed: engaging, believable and appealing. They’re joined by Alex Kingston as River Song, making her second appearance in the series after 2008’s “Silence in the Library”. On top of that it brings back the Weeping Angels, the villains of the immensely popular and critically acclaimed Season 3 episode “Blink”. The difference in quality between this episode and the last (“Victory of the Daleks”) is so pronounced it is liable to give viewers whiplash.

The Weeping Angels are a remarkable invention, and are typical of Steven Moffat’s approach to Doctor Who. They are, in effect, the children’s playground game “What’s the Time, Mr Wolf?” (aka “Grandma’s Footsteps”) transformed into a monster. They can only move when no one is looking at them. Take your eyes off them for a second, or even blink – hence the title of their debut episode – and they can move towards you. They’re wonderfully creepy and about the scariest monster Doctor Who has ever featured. The problem is that they really did feel like a one-off monster in “Blink”. It was a great conceit, but kind of the conceit you could only do once. Putting them into a two-part sequel was a risky move.

This is where I think Moffat did something inspired, which was to steal liberally from James Cameron’s film Aliens. Aliens worked in part because it escalated the threat of Ridley Scott’s original film Alien. That film had one sleek insectoid killing machine roaming a starship, so Cameron had dozens of aliens roaming a colony. Aliens isn’t scary because the monster could leap out from anywhere, it was scary because the monsters could leap out of everywhere. That’s pretty much exactly what Moffat does here: the Doctor, Amy and River embark into an ancient, crumbling labyrinth to track down one angel only to discover there are actually dozens of them.

Of course riffing on Aliens means finding some space marines. In typical Moffat fashion they’re not just soldiers but priests. We never find out precisely how this works, but they’re a bunch of armoured, well-armed clerics led by Father Octavian (the always solid Iain Glen). It’s a nice, slightly surreal touch that adds a lot of colour to what would otherwise have been dull, ordinary soldiers. It’s also a nice, albeit unexpected way to emphasise the Doctor’s nature as a man of science – some of the David Tennant episodes were making him positively messianic. Here he’s inadvertently offended a priest with his offhand anti-religious comments.

Aliens is not the only text being shaken upside-down for loose change. An extended sequence sees Amy menaced by a video recording of an Angel and somehow infected by it. It’s all drawing liberally on Koji Suzuki’s Ring, and adds yet another level of horror to the Angels as a monster. In their first appearance it was vital to stare at them at all times, and never even blink. In “The Time of Angels” this is transformed into needing to stare at them but also making sure not to stare at their faces, unless you get an Angel inside your head and start to die. It also introduces the idea of a monster that can kill you from inside a television set – as presented to a nation of children from inside a television set.

Even the regular Angels are particularly nasty here. In “Blink” they simply transported people back in time to feed on the resulting temporal energy. Here they’re getting all the energy they need from the leaking engines of the Byzantium, so are finding it much more enjoyable to just sneak up and snap people’s necks. They’re a particularly cruel and sadistic species, really. I’m not sure Doctor Who has one that’s crueller.

The episode also reunites the Doctor with River Song, his mysterious close friend from his own future. The first time he met her she died. Now, further back along her timeline, we discover she’s in prison for murdering someone. Moffat’s script doesn’t do a very good job of hiding the fact that it’s the Doctor she has murdered. While a poorly hidden development, it is certainly a provocative one.

As noted above, this was the first Season 5 episode to be shot, and you can really take this – and not the previous three episodes – as the start of Steven Moffat’s tenure as the series’ main creative. Both River Song and the Weeping Angels are refitted to enable subsequent appearances, something not so easy to do based on their respective first appearances. Audiences hear their first mentions of the Headless Monks, whose affairs will crop up again in Season 6. The central crash of the Byzantium was mentioned before, in Season 4’s “Silence in the Library”. The Church – later known as the Church of the Papal Mainframe – makes a few return appearances as well over the following years – most recently in Season 14’s “Boom”.

Beyond the sorts of odd and richly imagined story elements, however, “The Time of Angels” really is the first episode to fully resemble the kind of series Doctor Who becomes under Moffat’s guidance. Previous seasons by Russell T Davies had flirted with the Doctor as a romantic character; Moffat literally gives him a wife. Time travel becomes less of an excuse to get from story to story and more an integral part of the narrative. Ideas of the Doctor’s reputation and legacy, formed around the time Moffat wrote “Silence in the Library”, become a core subject of Matt Smith’s three seasons in the role.

Where Davies was happy to chain a season together via buzz words and ominous references – a “bad wolf” here, a “Torchwood” there – Moffat improvises complicated puzzle boxes. He is clearly flying without a net, and some of those choices will come to haunt the series when the time comes to try and neatly wrap it up, but in the heat of the moment this approach leads to some of the most inventive and jaw-dropping twists and turns the series ever had.

Science fiction, action, horror, time travel, great dialogue and wonderfully energetic performances: “The Time of Angels” remains one of my favourite episodes of Doctor Who.