The story unfolds gradually as emails between the two, divided up into a series of Instagram photo captions.
The photos themselves are largely taken from Hulin's 15-year career, though she's also cast models and made images specifically for the project. Sometimes they illustrate the text they accompany; sometimes - as is the case with all great Instagrams - they just evoke a place or a mood.
"I love Instagram," Hulin said from Providence, Rhode Island, where she lives. "I'm fascinated by this idea of everyone turning their lives into these daily visual narratives."
Hulin has always been into narratives, visual and otherwise; before she landed in Rhode Island she worked as a photo editor and writer in New York, and has shot images for Martha Stewart Living and the New York Times.
Six years ago, she began messing around with a blog that told the stories of two characters, Harry and Matilda.
She played around with it for a while, showing a few friends, but abandoned it to work on other projects. (You might've heard of Flying Henry, her children's book that went viral.)
Still, the characters stayed with her, as did the idea of using emails to tell their story. Last year, Hulin began working on a novel.
After finishing it earlier this year, however, Hulin realised that a whole host of digital artefacts could double as narrative techniques: photos, email accounts, personal websites even. She launched a newsletter and built Matilda a site for her wedding photography business. She also began going through her own photo archives and casting friends to play the principals for her Instagrams.
The result is an immersive digital narrative that makes Matilda and Harry feel eerily real. Not movie-real, necessarily - it's a bit vaguer than that. But real enough that Hulin has begun getting very earnest messages at Matilda's email account.
"It's like livestreaming a novel," she said. "It's like it became performance art."
This is not, needless to say, the first or only such performance on social media: Plenty of artists and writers have attempted the medium before, with varying degrees of success.
There have been several Twitter novels and novellas, including one by Cloud Atlas author David Mitchell.
Meanwhile, storytellers like Neil Shea and Jeff Sharlet have written striking narratives, fictional and otherwise, in their Instagram captions. But no one's done something quite so committed.
Hulin wasn't setting out to reinvent the genre, she cautions: she spent a year crafting this novel, and that work matters more to her than the novelty of how she's publishing it. (When the book finds an IRL publisher - which she expects it will soon - it might not even have many pictures in it.)
But it's given her an audience that's unusual for first-time literary fiction, and an experience that's unheard of for a first-time novelist. Hulin said a couple of "dicey" plot points were coming up soon and she didn't know how readers would react.
"I like waking up and seeing what people have said. It's very fun," she said. "But that one I might post at 3 in the morning."
