Premee Mohamed is an Indo-Caribbean scientist and speculative fiction author based in Edmonton, Alberta. Her new book, A Broken Darkness, out today from Solaris, is the sequel to 2020’s Beneath the Rising, a heart-warming adventure about two friends bonding over a clean energy project while negotiating with ancient evil extradimensional monsters who brutally kill people and want to subjugate the entire world and… hmm. Maybe ‘heart-warming’ isn’t quite the right word.

After Beneath the Rising came out, readers contacted me excitedly about northern Africa and the Middle East. “When did you visit?” “Which tour company did you use?” “Where can I actually find a hidden word of power?”

Folks, I’ve never been anywhere near there. I’ve only left North America a couple of times! But like a lot of writers, I love research, and I live for those moments when I discover some weird reference and can find a way to insert (okay: shoehorn) it into a story!

In A Broken Darkness, Nick Prasad is just getting used to the fallout of the first book: new job, new home, new relationships to his family. The end of his oldest, closest friendship with prodigy scientist Johnny Chambers. The entire world racked with paranoia (although is it really paranoia if you’ve discovered that everything is absolutely out to get you?). The only good thing about current events, Nick thinks, is that even though he and Johnny almost died in the effort, the world is safe. All the doors to other dimensions are shut and locked.

On the other hand, if you’re dealing with habitual liars on both sides, the doors may not be as locked as they seem…

Some of the interesting things in A Broken Darkness came from research I did for Beneath the Rising, but were too far away (geographically or narratively or both!) to fit into the first book. In the second book, I was determined to give them a good home!

Edinburgh and the plague tunnels. On my first trip to Edinburgh, I toured Mary King’s Close, the ‘built-over’ streets under the Royal Mile. Apparently because of these subterranean houses, tunnels, and other structures, Edinburgh kept having outbreaks long after nearby areas were plague-free. The guide chatted breezily about how many people living in the dense, rat-infested area had gotten infected and died there… and (far worse) how many sick people had likely been brought there by fearful neighbours or relatives to die. I couldn’t stop thinking about the tunnels and eventually worked it into A Broken Darkness, getting Nick and Johnny stuck down there with something after them. In every plague in history there have always been people who stayed put selflessly taking care of the afflicted… and there have always been people who chucked sick people out a window and shouted ‘STAY AWAY FROM THE REST OF US!’

Caves of giant crystals. Crystal caves, of course, are not fantasy set pieces; they’re real and several have been discovered worldwide. This initially seems to be the case in A Broken Darkness – Nick and the others find themselves in the Andes, cautiously entering a cave with crystals the size of skyscrapers. (With… writing on some of them? Not suspicious at all!) The specific conditions that allow real crystal caves are almost vanishingly rare, and took a long time for researchers to figure out. For example, the huge gypsum crystals in the Naica cave in Mexico developed while submerged in hot, supersaturated calcium sulphate-rich water and (most importantly) very slow or non-existent current. Under these conditions, crystals nucleated minimally, gathering the dissolved gypsum into a few huge crystals rather than numerous smaller ones. Each crystal, as far as scientists can calculate, took around a million years to form naturally. (Although with magic involved, that calculation would have been much harder. And, of course, these crystals didn’t form naturally.) Nick’s first clue that it wasn’t a natural crystal cave should have been that they didn’t drown when they discovered it!

Human sacrifice. In both novels, the main difference between their world and ours is that, of course, magic is real for them. In most fantasy books this would require developing a magic system: rules for the use, generation, and cost of magic. But one thing I always liked from older cosmic horror was a minimum of rules, especially the use of human sacrifice to ‘give power’ to the villains. What could be more horrific? A struggling victim, an implacable executioner, the knowledge that your death would do no good at all, only strengthen an evil, ancient being that would proceed to grind human civilization into raspberry jelly. Real civilizations around the world have historically performed human sacrifice for religious purposes, prophecy, as part of warfare or vendetta, as an alternative to imprisonment, and so on. What if, I thought, some of those were meant for the Ancient Ones – but the practitioners told everyone that they were for a different god? I sneaked this in as an anecdote in which supposedly Julius Caesar himself reports that one druid in Roman-colonized Britain is continuing human sacrifices long after others have stopped. Of course, this druid is really dedicating his sacrifices to Something Else.

I learned a zillion other things that I wanted to put into both books (monolith circles! possessed stones! haunted cathedrals!), but just couldn’t make them work. That’s the problem with research: not that there’s so much of it, but that you have to pick and choose not even your favourite bits but the bits that work for the final story. Maybe I’ll find somewhere to put the leftovers someday. (Can anyone say ‘spinoff stories’?)

A Broken Darkness is out now from Solaris; click here to order from Amazon.co.uk