"Cold War" is something of a love letter to the Second Doctor's era. Set on a submarine with no chance of escape, it nods back to many classic Doctor Who stories in which a base is under siege from a malevolent alien presence, and the Doctor is attempting to broker a peace between two hotheaded opponents.

And of course it sees the return of the Ice Warriors, albeit in a setting that will have seemed impossibly futuristic to the 1967 audience before whom they first appeared, for the appearance of a Sony Walkman if nothing else.

Here are a few things to keep an eye out for, the next time you watch:

(The episode is available on iTunes and Amazon.)

Although writer Mark Gatiss was keen to reintroduce one of classic Doctor Who's most notable monsters, Steven Moffat took some convincing. In an interview for Gallifrey One, he revealed that, while enjoying the stories they originally appeared in, he was worried they wouldn't make the transition to modern Doctor Who well: "It was Mark Gatiss’s idea and it was very much his pitch – he’d been pitching for Ice Warriors for a while. I wasn't tremendously persuaded. I'll be honest: I thought they were maybe the default condition for what people thought of as rubbish Doctor Who monsters – things that moved very, very slowly and spoke in a way that meant you couldn’t hear a word they said."

"Mark came up with a couple of very clever ideas, which he pitched to me over the phone in what was meant to be a Sherlock conversation. He had a couple of really stormingly good ideas, and it’s a great episode, an absolute cracker of an episode."

When the Doctor says, "Just this once, no dissembling, no psychic paper, no pretending to be an Earth Ambassador" he's referring to the events his Third incarnation took part in, during "The Curse of Peladon," during which he and his companion Jo Grant gatecrash an interstellar convention, and are mistaken—by Ice Warriors—for the delegates from Earth.

If the events in this story were true, this would mark the third time in 1983 that the world had stood on the brink of outright nuclear war. In November, NATO undertook a command post exercise called Able Archer, which simulated what would happen if conflict escalated right up to a DEFCON 1 nuclear attack. It was so realistic that some members of the Soviet Politburo believe the exercise to be part of a genuine plan to attack, and set their own armies on high alert. This was only called off when the exercise ended after five days. Captain Zhukov even refers to Able Archer early in this story, calling it "sabre rattling" on NATO's part.

A month earlier, a Soviet early-warning system suggested that intercontinental ballistic missiles had been fired from US bases towards the USSR. The warning was correctly identified as a false alarm by Soviet Air Defence officer Stanislav Yevgrafovich Petrov, who single-handedly prevented the launch of a retaliatory attack that would have inevitably started a nuclear war.

This episode contains two Doctors among its cast, and a potential third. Matt Smith aside, there's David Warner as Grisenko. David played an alternative Third Doctor in the Doctor Who Unbound series by Big Finish ("Sympathy For The Devil" and "Masters Of War"). And then there's Liam Cunningham (Captain Zhukov) who was in the running to play the Eighth Doctor in the 1996 Doctor Who TV movie.

Mark's original script had something in common with Terminator, in that Skaldak was intended to be a time-traveler coming back from the 31st century to stir up a nuclear apocalypse, so that he could prevent mankind from invading Mars in the future. Grisenko was intended to be a villain, seeking to convince the Ice Warrior to serve the Russian cause. Skaldak's methods including mind control over the Doctor's companion—at that point, a Victorian governess called Beryl—and the final resolution would see him killed by a Russian submariner, with the remaining crew, the Doctor and Beryl escaping to a British submarine called the Redoubt.

https://www.youtube.com/watch?v=MceRuUTwCGs

The names of the Russian crew are derived from several sources, both historical and literary. Stepashin is named after Sergei Stepashin, Prime Minister of Russia under President Boris Yeltsin; Zhukov was named after the Red Army General Georgy Zhukov, who helped liberate Europe during World War II; Onegin comes from the 1825 novel Eugene Onegin, by Alexander Pushkin.

The events in this story share a few common points with "The Ice Warriors," the first time the Doctor, in his second incarnation, met these martial Martians. There's a frozen body in the ice, a scientist is patiently waiting for it to thaw, believing it to be some kind of prehistoric mammal, and someone is too impatient to wait:

https://www.youtube.com/watch?v=wwrsYIl_5DA

The Doctor and Clara are the unwitting victims of the TARDIS defence mechanism called HADS, which stands for Hostile Action Displacement System. This had previously seen action in the Second Doctor story "The Krotons," in which the ship is under attack from a dispersion jet. Although it looks as if it has been destroyed, the TARDIS soon returns, once the threat has gone.

The Doctor mentions some of the things that can trigger the HADS, "Gunfire, time winds, the sea." Time winds are a recurring Doctor Who idea that go back as far as the Fourth Doctor story "Warrior's Gate". Certain time sensitive species, such as the Tharils, can make use of eddies in the Time Vortex to create glitches in space-time that allowed them to travel to other locations. In "Silver Nemesis," the Seventh Doctor encountered Lady Peinforte, who claimed to have ridden the "winds of time" from 1638 to 1988. Jack Harkness was killed by the time winds while hanging on to the outside of the TARDIS in "Utopia", Clara Oswald attempted to use them to cook a turkey in "The Time of the Doctor". The only species who have appeared to be capable of withstanding the effects of this temporal radiation ared the Reapers, who terrorised Rose Tyler's family after she altered history to save her father's life in "Father's Day."

Also, there's a deleted scene from "Daleks in Manhattan" in which the Tenth Doctor says he and Martha can travel "wherever the time winds take us," suggesting Gallifreyans view the time winds in the same way sailors view tides and currents.

Professor Grisenko is a huge fan of '80s electropop, which will have been hard to get hold of for anyone on his side of the Iron Curtain, hence the line "Got a friend who sends me the tapes." While he and Clara bond over "Hungry Like the Wolf" by Duran Duran, the first song we hear him enjoying is the 1981 hit "Vienna" by Ultravox, famous to UK pop fans for being one of Britain's most popular singles that never made it to No.1.

https://www.youtube.com/watch?v=xJeWySiuq1I

And to answer his impassioned plea, yes Ultravox did split up, in 1987. But they reformed in 1992, and again in 2008, and are still going.

NEXT: "Hide"

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