Caitlin Starling: Five Things I Learned Writing Last To Leave The Room

The city of San Siroco is sinking. The basement of Dr. Tamsin Rivers, the arrogant, selfish head of the research team assigned to find the source of the subsidence, is sinking faster.

As Tamsin grows obsessed with the distorting dimensions of the room at the bottom of the stairs, she finds a door that didn’t exist before – and one night, it opens to reveal an exact physical copy of her. This doppelgänger is sweet and biddable where Tamsin is calculating and cruel. It appears fully, terribly human, passing every test Tamsin can devise. But the longer the double exists, the more Tamsin begins to forget pieces of her life, to lose track of time, to grow terrified of the outside world.

With her employer becoming increasingly suspicious, Tamsin must try to hold herself together long enough to figure out what her double wants from her, and just where the mysterious door leads…

1. I don’t understand physics.

Here’s the hook for Last to Leave the Room: the city of San Siroco is sinking, and Dr. Tamsin River’s basement is sinking faster. It’s mysterious, it’s visceral, it’s unnerving – and, it turns out, it was wildly effective at showing me just how much I don’t understand physics.

An actually-sinking city would likely be caused by something like a gigantic sink hole. Sink holes, well, sink – the ground underneath a building collapses in on itself, and the building goes down with it. But for my mysterious, creepy vibes, I wanted the buildings to stay put. It’s the subway tunnels that are getting lower. The pipes and fiberoptics running below the city streets.

The floor of Tamsin’s basement.

At first, I tried to figure out a way it could work. But finding a plausible scientific explanation for the situation, while satisfying my newfound anxiety about my understanding of physics, would have actually run counter to the whole point of the book. Instead, I had to lean in; I had to make the problem I was facing the characters’ problem. It isn’t just that the city is sinking.

It’s stretching, and there’s no explanation for how. And that means there’s something much worse afoot.

2. Soylent gives you bad GI issues.

Tamsin is employed by a company called Myrica Dynamics, an ambiguous tech corporation that’s a little bit Amazon, a little bit Google, and a whole lot “companies you didn’t realize were all actually owned by the same shadowy conglomerate.” Tamsin herself works in a shady R&D department with a very roomy budget, and she lives a very tech-industry lifestyle; fancy ride-ordering app, fancy smart home, fancy meal-kit subscription… and a penchant for drinking meal replacement shakes anyway, because who has time for cooking? Especially when you’re trying to figure out why an exact physical copy of yourself has just walked out of a door in your basement that wasn’t there last week?

It turns out, though, that if you drink most of your meals, your intestines might take up arms against you. Soylent very notoriously gave a whole lot of people a whole lot of GI issues. Apparently, humans aren’t actually perfect inventors, and our convenient replacements for things like food don’t always behave the way we expect them to.

Hey, wait a minute. That sounds thematically relevant.

3. Prosthetic limb tech is super cool!

I don’t want to spoil anything, but there’s a character with a prosthetic limb or two (and there aren’t many characters, so I bet you can figure it out inside three guesses). Last to Leave the Room is set five minutes into the future, and with Myrica Dynamics backing the characters, I decided to press fast-forward on prosthesis technology a little. But I didn’t have to push too far! Researchers and specialty companies are already building arms that can be controlled via nerve impulses, and microprocessor knees that do the fancy work of figuring out how to help balance the load of a body.

But while all that’s nice, it’s a lot for every day. So I also looked into day to day life: modifications that character could make to their apartment for accessibility, how much they’d actually wear their prosthetic limb(s) around the house, what other options they’d have. I did a lot of reading first hand accounts and lurking on forums, and I hope that the life I’ve constructed for this character reads true.

And the overall upshot? Adaptive tech, which I first got a taste for while writing The Luminous Dead, continues to be incredibly neat. 

4. Situs inversus is also super cool… and creepy.

Bodies, human and otherwise, follow general patterns and layouts. But within those layouts, there’s a surprising amount of room for variation. The farther from your core they get, the more your veins and arteries get creative with their organization (to the point where there’s been some work on identifying suspects by the vein patterns in their hands and forearms). People can have extra “accessory” bones, or variants of musculature. In fact, part of the benefit of cadaver dissection in medical school is exposure to a real body, as opposed to the theoretical “average” body.

And did you know that about 1 in 10,000 people have their internal organs partially or entirely mirrored compared to standard human anatomy? Most of the time, it doesn’t cause any issues, and you wouldn’t even know you had it unless you had thoracic or abdominal surgery. (Occasionally it comes with some heart defects; you find out relatively quickly in that case.) I’d heard of situs inversus at some point in my past, probably around when I learned about fibrodysplasia ossifcans progressiva, which wormed its way into my last book. The idea stuck around, hovering in the background of my brain, until I started writing Last to Leave the Room and realized that a scientifically-minded person would, of course, want to know exactly how identical her doppelganger was to herself.

So give that bitch an ultrasound machine! She just might not like what she finds out about herself…

5. Sometimes you just have to give your main character’s hair its own arc.

Tamsin carefully controls everything in her life to create a certain effect. Her relationships, her reputation, her appearance. When we first meet her, she’s dressed exquisitely, her curly red hair is perfectly maintained, and she wears full-face make up and heels every day. This being a horror novel, she gets more than a little scuffed up before the final pages.

In the last phase of edits, my editor focused in on one specific detail: Tamsin’s hair. I’d made passing references to it getting a bit gross and tangled over the course of the plot, and my editor suggested I amp it up. Really track it, and, essentially, give Tamsin’s hair its own plot arc that moved in lockstep with Tamsin’s mental health (or lack thereof). What starts as distraction devolves into neglect and finally into chaos.

It’s a small detail, but tracking the state of Tamsin’s hair made me pay closer attention to Tamsin’s mind, and all the other little details of her environment. Her forgetting to take showers snowballing into forgetting salon appointments reinforced the less tangible aspects of her decline. Sometimes, it’s the small things that make the horror more real–and more terrible.

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Caitlin Starling is the nationally bestselling author of The Death of Jane Lawrence (2021), Last to Leave the Room (2023), and the award-winning The Luminous Dead (2019). Her other works of genre-hopping horror and speculative fiction include Yellow Jessamine and a novella in the Vampire: The Masquerade collection, Walk Among Us. Her nonfiction has appeared in Nightmare, Uncanny, and Nightfire. Caitlin also works in narrative design, and has been paid to invent body parts. She’s always on the lookout for new ways to inflict insomnia.

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