Unholy Blood: A Horror Novel

by Ian Gielen

A hidden cave. A Halloween party. A nightmare waiting to unfold.

While exploring off-trail on Coon Mountain in the breathtaking Adirondacks, college seniors Jack and Mason stumble upon a mysterious cave, concealed behind a curtain of tangled vines. Excited by the discovery, they return days later with their friends for a once-in-a-lifetime private Halloween party in its shadowy depths.

But beyond the laughter, booming music, and crackling campfire, something stirs. Something ancient. Something ravenous. Their arrival has awakened a presence that has waited in the shadows for years—hungry for its favorite meal.

This Halloween, the party ends when the screaming starts.

Genres: Horror

207 pages, ebook

First published August 1, 2025

About the author

A horror fan since childhood, Ian embraces his inner geek with pride, his dedication displayed in the intimidating collection of horror novels and video games that threaten to take over his living space.

He is mad for all things Alien, Star Wars, and cats, his furry companions always there to keep him company as he scribbles down his latest ideas.

He's a father in Melbourne, Australia, sharing his home with his partner, two stepdaughters, and four cats. The sheer number of furry and human companions in his life might be enough to drive anyone a little crazy.

You can follow his writing journey on Facebook at - Ian Gielen - Author

Reviews

[Peter Topside · Rating 4 out of 5]

A very, very solid creature feature from Ian Gielen. Fantastic use of the cave system environment, also utilizing several different creatures and many horror elements well. I consider The Descent one of the best horror movies made in recent memory. The scariness and gore that it brought was rivaled by few others, and this brought me back to that. The other, notable, aspect of the book was how each of our vintage, horned up, party going teenagers got an adequate amount of time and development, as their stories intertwined with one another. The cover also made me knees shake, as it reminded me of the very first version of my Preternatural book, some 28 years ago and originally titled 'A Drop of Blood.' But the creature at the end that I envisioned is almost exactly as depicted on this gorgeous cover, made me reminiscent. Fans of creature features, teenage slashers, and 90s horror will find an abundance to like here.

[Stephanie · Rating 5 out of 5]

Unholy Blood takes you deep into the caves of the Adirondacks. Out for a mountain hike, college seniors Jack and Mason stumble, quite literally, into a cave hidden by vines. Jack thinks it’s the perfect place to have an epic Halloween party, the last of their college career. When the day arrives, they bring their girlfriends and two other friends. What starts as a fun, raucous party takes a turn towards the terrifying. The friends find themselves trapped with no cell service, no one knows where they are, and what’s worse, they aren’t alone.

This book is fraught with claustrophobic tension. Ian’s descriptions of the cave, the narrow passages that can barely be squeezed through, and the labyrinthine maze the friends work to find their way out of made me incredibly uncomfortable. There are also moments of startling beauty and hope. The characters are real and relatable, flaws and all. You feel their joy when the party starts and their utter terror as the night progresses. For those of you that are afraid of small, dark spaces, be forewarned! But don’t sleep on this book. This is one Halloween party you don’t want to miss!

[Milt Theo · Rating 4 out of 5]

"Unholy Blood" blends deep cave horror with a creature feature, to tell an immersive and claustrophobic story of visceral thrill and bloody carnage! Although TBH it doesn't break any new ground, it successfully captures the found footage atmosphere (lots of banter, a slow beginning, young people partying, ending up getting hunted) in a B-movie setting (creatures whose origins are never explained, a generous mix of sex and death, over-the-top killings), with an ending which won't disappoint any horror fan!

I especially liked the second part of the book, intense and graphic in equal measure. I disliked the repetitions (people often sharing information, despite readers being already aware of it), and the uneven pacing between the action scenes. That said, the heroics and the killings were quite well done. And the ending is, to repeat, very good.

Recommended!

[David-Jack Fletcher · Rating 4 out of 5]

There is a lot to love about this book. I am a sucker for creature features, and bats are always pretty creepy. At times, I got Jeepers Creepers vibes, just with how the creature was mostly instinctual but had some kind of awareness of its own history and desires. It was a nice touch to include some POV of the creature.

Reminiscent of The Descent, this book will take you deep beneath the earth, and unmask the horrors thriving down there.

I did find a few areas a little repetitive and perhaps drawn out, and the characters could have been developed a bit more to feel ‘real’. These are just little things and completely personal opinions of what I like to see in books.

Overall, I firmly believe the majority of readers will absolutely love this book, and I recommend any horror fan to check it out!

[Daniel Nobles · Rating 4 out of 5]

Overall a great story, just a bit long at parts and what felt a bit drawn out. This story feels like a mixture between The Descent, Pitch Black, finishing with 30 Days Of Night vibes.

[Kati Chastain · Rating 4 out of 5]

Unholy Blood is a dive into darkness—literal and psychological. Ian Gielen crafts a tale plunging readers into a forgotten cave where something ancient, mutated, and very hungry has just woken up.

The story kicks off with a group of college seniors who choose the worst possible place to throw a Halloween party: a mysterious, untouched cave. What starts as a night of thrills quickly spirals into a nightmare, as the group finds themselves lost in a labyrinth of claustrophobic tunnels, stalked by a bat-like predator that has waited decades to feed.

Fans of The Descent or gritty '80s creature features will feel right at home here. If you love survival horror with a nostalgic edge and a taste for gore, Unholy Blood delivers the goods.

[Christine · Rating 5 out of 5]

review to come.

[Emily Haynes · Rating 5 out of 5]

An accidental discovery of a cave led two friends to have a party in this secluded place. There is something hiding waiting patiently for its food. Amazing characters you root for. Creatures that make you cringe. Full of hope, heartache, suspense, and horror.

[Don Anelli · Rating 5 out of 5]

This was a fantastic effort that has quite a lot to like about it. The intriguing setup provides a fine way of getting into the cave, where it spends the first half delving into the friend group, preparing for the party. As we see the group going through their series of studies, school work, and general state of living in their relationships helps to give this the kind of starting point which gives this a lot to like, getting in depth with the couples who are going through the struggles of college life and extracurricular activities between them as well as the first stages of the party being set up for the end of the week. This might end up feeling a bit too long in the first half, with the scale of the group going through the motions as it does with the stragglers getting to see their different activities throughout the week before the party, when the more important part is the celebration. Still, it's a minor issue since it gives us a chance to know the group before then.

Once it gets to the party and we see them getting to the cave, this turns into an effectively enjoyable and likable creature feature. The history of the cave and the nature of the creatures living there provide a strong starting point for what's happening as they begin to be attacked, leading to the frantic encounters within the tunnels and underground caverns of the mountain. We get just enough in that regard to make the different encounters feel quite dark and chilling as they circle the group, slowly picking them off one by one in a creepy location, causing plenty of carnage and bloodshed along the way as the confrontations display an ingenious ability to transform victims into more like them. It's got a feverish quality that helps to overcome the sluggish first half, getting there and creating plenty of fun that makes everything a great time overall.

4.5/5

[Andrew Wilkes · Rating 4 out of 5]

These aren't your grandma's vampires, and, they sure don't sparkle! This book was a fun ride into the depths of a mountain where everything can, and, will try to kill you. I love how the book's chapters follow different characters through their journeys of survival, and, even, the navigation of every day college life, and, young adult issues. There are chapters, that, even, follow around the "antagonists", we'll call them. I didn't think you would get much character depth, but, it is definitely there. You find yourself really feeling for a couple of the characters, and, rooting for the others. I absolutely love creature features, but, I thought this would be all horror, and, no gore, but, I was wrong. It gets pretty bloody. If you like tales of survival, creatures, and, the fear of an unknown expedition, all wrapped in the charm of a story about college buddies, who, just wanna have fun, and, get laid, then, I recommend this book!
🦇🦇🦇🦇/5

[MaRissa Williams · Rating 4 out of 5]

Thank you for the opportunity of letting me read this book.

Details - Brilliant.

This gave me Jeepers Creepers vibe mixed with found footage horror.
This is disturbing, and I loved it.
It definitely triggered my claustrophobia, and it was very unsettling but I was still hooked nonetheless.

I really liked the characters, even though there were a few I wish would have had a good ending.

Jenny was one of my favorites. She was relatable to me as I am close to the same type of person that she is. I also loved Christina and her strong willingness to live. I loved the banter between Jack and Mason, it was very entertaining.

I liked that it wasn’t fast paced whereas a lot of books are these days, I really liked it.

I received a free copy of this book via Booksprout and am voluntarily leaving a review.

[Angel Medina · Rating 4 out of 5]

This is the second book I've read by Ian. Unholy Blood is a great creature horror read, which is one of my favorite tropes. He does a wonderful job with the cave environment, which I also enjoy. Once the students get into the cave, that's when SHTF! I couldn't stop reading despite life saying I had to. I needed to see how this finished. Ian managed to make me cry toward the end, as it's not quite the traditional happily-ever-after ending. That's all I can say without spoiling.

The only reason this book misses out on a perfect rating is that the beginning is a bit slow. It does build the world and characters, so I'll get it that. When it comes to favorite characters, it has to be Jack. The man might be arrogant, but he is protective of his friends.

Overall, if you enjoy cave horror, this is a great one to pick up!

[Dion Smith · Rating 4 out of 5]

I love a good creature feature, especially when the creature isn’t just some dumb animal, and there are parts from the point of view of the creature, which I always love, and that cover is great.

This one reminded me of The Ruins (both book and movie) and the 2005 movie The Descent, with it being set in a labyrinth cave system, but the dynamic between the people is completely different, and the scenery changes a bit which I liked.

I would have liked to have seen the creature sooner, but the writing was really smooth, and easy to read.

If you like a good trapped underground with creatures then I recommend this one.

[Dale Robertson · Rating 4 out of 5]

3.5 stars round up to 4. It's a good creature feature story with a claustrophobic atmosphere. There was a part in the story where another creature appeared, did its thing, then disappeared, it was never really explained (apart from being named as a local myth) and it felt a bit out of place in the overall story. Maybe it was something to do with that area of the world and the writer wanted to add it in.

The book was well written with short chapters, which made it a quick read for me. It also has an open ending which could potentially lead the way for a sequel.

[Breanna · Rating 5 out of 5]

The perfect book for spooky season

Halloween night is known for parties and scares. But when a group of college students decide to have a small party in a hidden cave, things go from fun to devastating. Creatures that are hunting, dead end tunnels, and no way to escape. One bite from a bat and their lives changed forever.

[Chelle · Rating 5 out of 5]

An intriguing tale that sucked me in from the start, a fantastic mix of love, friendship, monsters and chaos.

My heart was pounding, and in places I am sure I even held my breath.

A Well written and exciting journey, following 6 friends and the Halloween party from hell.

⭐️⭐️⭐️⭐️⭐️

[Megan Russ · Rating 4 out of 5]

A true cave dive

Fans of Descent will find a welcome cave within these haunting pages. My only dislike were the out of place spicy scenes. It would have been a five star. It just felt so out of place with the rest of the story.
Perhaps we should all think twice before we go cave diving.

[Paige Leiby · Rating 5 out of 5]

A group of friends plans one last college blowout for Halloween in a hidden cave where, deep within, something ancient slumbers. When it awakens hungry, this will be the party to end all parties - literally.

Ian Gielen leads his characters deeper and deeper into abysmal darkness with relentless horrors, and you, the reader, are helplessly along for the unholy ride.


I'm truly excited to read more of Ian Gielen!

[Shanda · Rating 4 out of 5]

College seniors Jack and Mason stumble upon a cave while hiking in the Adirondacks. They return a few days later, on Halloween night, to have a Halloween party with their friends. What was meant to be good times filled with friends and laughter turned into a fight for survival.
This was a pretty decent creature feature giving off Jeepers Creepers and the Decent vibes. But there were several parts that were a little boring and long winded. I would have loved some back story on the creatures and maybe the cave system. The second half of the book kicked up the action and gore and I enjoyed the ending. All in all decent read.

[dawn · Rating 5 out of 5]

Omg, this book had all my emotions out. I started this book, not knowing any of Ian's work but the cover caught my eye. As I was reading it, I was starting to lose it cause it was a bit slow, at one point I was gonna give up, but glad I didn't... I really enjoyed this book, one minute I was bored then I was shouting at my phone for them to run (I no, they can't hear me) but by the end, I was crying.. I hope there's gonna be a second book, I would like to see whether anyone went back for the bodies....

[Robin Ginther-Venneri · Rating 5 out of 5]

Unholy Blood: A Horror Novel
By: Ian Gielen
Publisher: Independently Published
Published Date: August 1, 2025
ASIN: B0FDWNB211
Page Count: 206
Triggers: Claustrophobia, gore, death, body horror, some sexual content, cave-induced existential dread
Star Rating: ⭐️⭐️⭐️⭐️⭐️
Skull Dread Rating: 💀💀💀

I laughed, I screamed, I considered canceling all future hiking plans. Unholy Blood is messy, atmospheric horror perfection, and I am hereby declaring myself a forever-reader of whatever nightmare Mr. Gielen dreams up next. Just, like… maybe give us a rope ladder next time, yeah?
What Did I Just Walk Into?
A Halloween party in a vine-covered death trap, apparently. Six college students decide that the best way to spend All Hallows’ Eve is to rage inside a cave they found while hiking—because what screams “good life choices” like mixing alcohol, darkness, and an ancient monster with a serious hunger problem?

Here’s What Slapped:
The cave setting? Absolutely feral. I could feel the walls closing in. If you’re even mildly claustrophobic, this book will have you dry-heaving into your favorite throw pillow.

Creature POV chapters. Yes, you read that right. We get to feel the hunger.

Mr. Ian Gielen doesn’t just build atmosphere—he buries you alive in it. I practically needed a headlamp to finish reading.

Jenny and Christina. Jack and Mason’s banter? Pitch-perfect horror-comedy bromance.

The pacing in the second half goes from “student film” to “OH GOD THEY'RE COMING THROUGH THE WALLS” in record time.

Also: blood. Gallons. Unapologetic, arterial, and fabulous.

What Could’ve Been Better:
The first half lingers just a touch too long on college life. I get it, Jack’s failing Bio and Christina is over it. But can we unleash the beast already?

Some of the characters were flirting with horror-movie cliché territory... but thankfully, Mr. Gielen lets them breathe just enough to earn our panic tears when they start dropping.

Repetition in the “where are we?” panic moments. Listen, I was lost too, but maybe less retracing and more monster-chasing next time?

Perfect for Readers Who Love:
The Descent, but with more beer and bad decisions
Creature features that lean into the bloody chaos
Horror stories that double as cautionary tales for why you don’t party in places with zero cell service
The kind of immersive survival horror that makes you question whether spelunking should be legal

Reviewed by Robin for Robin’s Review

[Savannah · Rating 5 out of 5]

Unholy Blood is the first novel from Ian Gielen, an Australian author already taking the world by storm with his debut novella, Saving Tommy. With some gorgeous formatting by Jyl Glenn (seriously those bats are gorgeous) this book is a treat for the senses!
Readers are transported to the Adirondacks, a mountain range in New York riddled with caves and legends. Two college seniors get the bright idea to take a frickin CAVE and turn it into the location of a rave. For Halloween of all holidays. Pure genius…not! There’s an ancient evil in the cave, and it is not a fan of being woken up by a bunch of drunk college kids and I mean…fair. It’s a special point in your life when you start identifying with the monsters because dang it, i just want some good quality sleep.
Ian carries forward his momentum from Saving Tommy and asks the question, sophomore slump who? Unholy Blood is darker, gritter, and more immersive. I cried internally every time I had to put it down to do actual work like laundry. A travesty! This novel will make you equally want to sit and savor, while also tearing through at a breakneck pace because you need to know what happens!
I loved the atmosphere—I’ve been in caves before and while they’re fun to visit, it’s easy to imagine just how much could go wrong there. The darkness, the echoes, the borderline claustrophobia…shudders. Ian did a fantastic job putting readers in the story, delighting and terrifying our senses with every page. Take Hollow, dial it up to 11, and squeeze readers into an inescapably narrow passage of terror, and you have Unholy Blood. The tension, the drama…delicious!
This is one creature feature you don’t want to miss! Unholy Blood releases Aug 1, and it better be hitting your Kindle.

[Drew Moyer · Rating 4 out of 5]

As you can probably tell by this freaking awesome cover, Ian's first full novel is a fun, bloody, gory creature romp. If you haven’t checked out his debut novella Saving Tommy, definitely check that out.

We follow a group of college kids—jocks, cheerleaders, nerds—who discover a cave and decide they want an experience they’ll never forget. What do they do? Have a Halloween party in an unexplored cave. what could possibly go wrong?

Everything goes wrong, of course. Mutated bats and a cave in for starters. Then things get even WORSE! A gnarly blend of creature horror, claustrophobic survival, with a few surprises thrown in, this book delivers thrills, chills, and BLOOD! Lots and lots of blood. And don’t even get me started on how claustrophobic this made me. I found myself holding my breath when the characters were squeezing through tight gaps in a desperate hope of finding any escape.

While I did have a blast reading this book, a few of the scenes of the characters getting lost did get a bit repetitive. Still, this is a fun ride and absolutely delivers everything us blood thirsty horror fans crave!

[Chris Heinicke · Rating 5 out of 5]

A group of six teenagers set out for a night of epic fun to celebrate Halloween. Packed with alcohol, snacks and camping supplies, what promises to be a night to remember soon turns out that way, but not for the right reasons. Taking place in a cave inside a cliff, an avalanche soon occurs, injuring two of the group. Leaving one member of the group to keep watch, the other three search for a way out.
But the six teens aren’t the lone occupants of the cave network. An unseen predator lurks within, and soon makes its presence known. What follows is an intense search for a way out to seek help, as well as a fight to remain alive as they soon find themselves the hunted.
I enjoyed the way Ian wrote an atmospheric story of survival, a kind of ‘who will make it out’ type story. The characters were well written, and although there were typical football stars and cheerleaders involved, they had depths breathed into them that made them not the typical cookie-cutter characters you might otherwise expect. While some readers may prefer a faster paced story, I found it gave me a chance to breathe, and get drawn in by the characters and location in which they were trapped.
5 out of 5 stars

[Micki-D · Rating 4 out of 5]

Giving off Jeepers creepers vibes mixed with the decent vibes. This cave horror is a creature feature you don’t wanna miss. It’s feels like one of my favourite b rate horror movies happening right one the pages before my eyes. While it might be a bit repetitive at times it was also graphic and intense the second half of the book is action packed and really picks up pace.

A Halloween party you won’t soon forget. A group of six teenagers are out for a night of fun to celebrate Halloween, a night then won’t soon forget. Packed with all the necessities snacks, alcohol, and camping supplies. They find the perfect spot inside of a cave.

What once was the prefect party soon becomes a fight for survival when an avalanche soon occurs, leaving two injuring of the six. Leaving one member of the group to keep watch of those hurt the other three search for a way out. Is there a way out? Can they find it before it’s too late? What else might be lurking in the dark depth of the cave?

[Mieke Janssens · Rating 5 out of 5]

A group of students decide to throw a Halloween party in a cave they’ve just discovered. Little do they know they’re about to awaken something dark… something ancient… something truly terrifying.

I really enjoyed this book. The growing sense of dread and claustrophobia creeps up on you with every page, tightening its grip as the story unfolds. The tension is palpable, the kills are bloody, and the creatures are downright horrifying.

Sure, the main characters make some questionable choices (and seriously, why do they keep falling asleep in the middle of the nightmare?), but that’s just nitpicking.

Don’t sleep on this one — it’s a chilling horror ride that’ll leave you gasping for air.

[Justin Boote · Rating 5 out of 5]

My first by Ian Gielen and definitely not my last!
A group of friends decide to have a Halloween party at a remote cave 2 of the friends stumbled upon. Alcohol and lots of fun. Until the entrance caves in leaving them trapped. Trying not to panic they split up to find an alternative exit. But unknown to them, something ancient and evil lurks in the cave and it's just woken up...
Great story by Ian, first introducing us to the characters then letting all hell break free when the trouble starts. One never knows who, if anyone, is going to survive-an excellent, claustrophic story, looking forward to more!

[jamie d mills · Rating 5 out of 5]

Once awhile a book comes along and reminds me of why I don’t do certain things. This is one was it. I would never go camping. This book is a cautionary tale of the dangers that comes from camping in a cave.

A group of friends decided to spend Halloween together in a cave. When things started going wrong, will they be able to survive the night?

It was a steady paced novel. The story from beginning to end was captivating and didn’t disappoint. I would highly recommend for those who loves creature books.

[Dan Mckeithan · Rating 5 out of 5]

A great intense story! Gielen take the reader on a submersive journey into the confined spaces of a cavern. His group of college partiers don't realize what they have stumbled upon and released.

It brings to mind the Descent in the way they have to explore the caves in the dark the challenges they have to overcome. If you like closed in spaces in the dark, not knowing what is surrounding you or where you're going, this is the story for you!

[K.L. Patrick · Rating 5 out of 5]

A thrill ride that expands on known Tropes. From the college students, and creatures, what in ways feels like a vampire novel turns into so much more. College kids find a cave and unleash a old long lost monster. A thrilling different take on the vampire story that will keep you guessing.

Five stars. A fun read my friend, I just want to know more about the creatures! Maybe in the future!