Molten Heart by Una McCormack and the History of Subterranean Fiction

Una McCormack’s Molten Heart sees the Doctor and company arrive on a world within a world. Fittingly, this idea forms the basis of a entire subgenre within the genres of sci-fi and fantasy…

But you might not have heard: it’s very underground.

Molten Heart

Dr. Una McCormack’s novel is the second in a trio of Doctor Who tie-in novels. The Thirteenth Doctor, Graham, Yaz and Ryan land beneath the surface of the planet Adamatine. They’re sent on a topsy-turvy adventure to recover the TARDIS and the missing father of a new friend. As they explore, it becomes very clear that the world within Adamantine is under an ecological threat with natives too stubborn to take it seriously.

Your world – most worlds – have a crust and loads of layers around a molten core. Not here. Here there’s…a sort of balloon inside, right in the middle. A bubble. An egg shell. Outside, on the planet’s crust, it looks like there’s nothing…Do you see? This is where the world is!


Molten Heart is very reminiscent of Doctor Who’s earliest days, especially in the opening chapters as they explore their new environment. The Doctor examines and speculates on what they find in a way that feels very Hartnell-esque. Indeed, in the best Doctor Who traditions, our regular quartet are split up for a large swathe of the story. Though the novel was written with relatively little information on the series, McCormack has naturally built upon the emerging mentor relationship between the Doctor and Ryan. New characters, particularly Ash and Quartz, get a lot of great characterisation and really help sell Adamantine’s interior as a functioning society with diverse perspectives. While the lean 193 pages means that certain character beats get resolved surprisingly early, the breadth of imagination on display makes the story feel a lot more substantial.

I got the chance to chat to Dr Una McCormack about Molten Heart last week. Check out my interview here.

Going Underground

Even if you’re not big on science-fiction, it’s a pretty safe bet that you’ve heard of Journey to the Centre of the Earth by Jules Verne. The 1864 novel popularised the nascent genre of subterranean fiction – stories set predominately beneath the surface of the Earth. While, strictly speaking, works in this genre don’t necessarily have to take place on Earth, the overwhelming majority of them do. I guess if you’re going to explore this idea, it’s more interesting to tell the reader that this is all happening beneath their feet. Plus “subterranean” literally means “beneath the Earth”. I guess the term for a story that takes place under the surface of Mars would be “submartian fiction” but in Doctor Who terms that would just be an Ice Warrior in a submarine. And we’ve seen it.

The genre’s earliest entries, published mainly in the centuries before the Enlightenment, mostly looked at the concept as a purely allegorical one. The most famous probably being Dante’s Inferno where Dante is lead through nine concentric levels of Hell beneath the surface of the Earth and emerging on the other side of the planet. The idea was generally used as a plot device to send an everyday protagonist to another world without having to address the problems of space travel. Such as Giacomo Casanova’s Icosaméron in which a brother and sister fall into an underground utopia run by hermaphroditic dwarves. Or in 1820’s Symzonia: A Voyage of Discovery which may have been authored by John Cleves Symmes Jr. – a vocal proponent of the “Hollow Earth” theory.

I declare the earth is hollow, and habitable within; containing a number of solid concentrick spheres, one within the other, and that it is open at the poles 12 or 16 degrees; I pledge my life in support of this truth, and am ready to explore the hollow, if the world will support and aid me in the undertaking. — John Cleves Symmes Jr.

Practically all of the genre’s early popularity can be attributed to the Hollow Earth concept. Quite simply, this is the idea that the Earth is either entirely hollow or at least very roomy. Though first proposed by Edmond Halley (of comet fame), it was later defended by Symmes who embellished it and posited that openings into the interior would be found at the poles. They weren’t. But that didn’t stop the idea from influencing Edgar Allan Poe in his only complete novel, The Narrative of Arthur Gordon Pym of Nantucket, or Edgar Rice Burroughs’ Pellucidar series.

Who’s Down There?

Since this is a Doctor Who blog, I could hardly fail to mention the multiple times that the Doctor has stumbled across buried civilisations. A list of every instance of our heroes finding hollow worlds would take ages. But I think the two most relevant examples to Molten Heart have to be 1978’s The Pirate Planet by Douglas Adams. The Doctor and Romana arrive on a hollow planet Zanak being driven around space by a ranting space pirate materialising around worlds and plundering its resources.

Funnily enough, I reviewed a 2017 novelisation of the The Pirate Planet over on BlogtorWho.

More recently, the two-part story The Hungry Earth and Cold Blood depicts a cavernous Silurian city several miles below the surface of the Earth. Building on the Silurian lore from the classic series, the story teases millions of Silurians sleeping beneath the planet ready to awaken and reemerge someday.

Journey to the Centre of a Genre

Once Verne’s work hit the shelves, the genre enjoyed a surge in popularity. Edgar Rice Burroughs, despite using John Carter to solve the space travel conundrum by having him astral project to Mars, kept Pellucidar going for almost fifty years. Across seven books, the series sees two friends burrowing into the Earth’s crust and exploring a world on the interior surface of the planet. As with Verne’s work, acknowledged as having influenced Burroughs, they discover prehistorical animals and primitive civilisations.

However, at this point you start to see more fantasy works exploring the idea of underground societies, including the kingdom of Angband in Tolkein’s Middle Earth stories, the Underland from The Chronicles of Narnia by C.S. Lewis and Eoin Colfer’s Artemis Fowl series.


You may have noticed how many of these stories involve secrets at the heart of the Earth and people travelling to find them. Where Molten Heart inverts the idea is, of course, having those inside the planet looking outwards. The idea of worlds beyond their own is ridiculed but some brave explorers prove them wrong and make a discovery that saves the day. In many ways, this story feels like a natural evolution of the genre, and naturally I’m thrilled that it’s in a Doctor Who story.

Further Reading

Hollow Earth : the Long and Curious History of Imagining Strange Lands, Fantastical Creatures, Advanced Civilizations, and Marvelous Machines Below the Earth’s Surface by David Standish

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