If you want some gory hard science fiction, you need to read Parasite

Mira Grant, author of the social media zombie series Newsflesh, is back with another tale of pandemics that threaten to transform humanity into shuffling, homicidal maniacs. Parasite is a spine-tingling, near-future tale of what happens when a new medical technology starts (literally) eating our brains.

The scientific premise of Parasite is simply terrific, and seals Grant's reputation as one of today's most exciting hard science fiction authors. In the world of Parasite, human allergies and other ailments have reached epic proportions because our obsession with killing germs and sterilizing every surface has left our immune systems weak. We've lost our ability to resist even a tiny bug. This scenario is called the hygiene hypothesis, and Grant does a great job dramatizing its effects.

Enter SymboGen, a biotech company of Genentech proportions, which has genetically engineered a parasite that solves the hygiene hypothesis crisis. It lives in the intestines, extruding medicines, birth control, and possibly other enhancers into its hosts' bodies. And it has the side-benefit of giving our immune systems something harmless to attack, thus keeping our immunity robust and reducing allergic reactions. SymboGen claims responsibility for eradicting most diseases, especially in developing countries.

The problem, as anyone who has read Jurassic Park might guess, is that when you genetically engineer something you never know what all that extra DNA is going to do. In the case of the SymboGen parasites, DNA borrowed from other organisms encourages the parasites to — you guessed it — climb out of the gut and into the brain. Cue the arrival of murderous "sleepwalkers," dead-eyed humans who are controlled by their parasites.

But our hero, Sal, is one of those people who owes her life to the parasite inside her. She's declared brain dead after a horrific car accident, but somehow the SymboGen parasite brings her back to life. The problem? Six years after her miraculous awakening, Sal still can't remember anything about her life before the accident — and she's developed a completely different personality from Sally, the woman she used to be.

We suspect immediately that Sal's weird mental condition probably has something to do with her parasite, but Grant plays coy, leading us through Sal's confusion and struggle to accept what's really happened to her. This means that the novel occasionally feels like a wasted opportunity. Instead of exploring what it would be like to have your mind transformed by a parasite, or even what it would be like to know that you owe your life to a giant gut worm, Grant focuses on minor details of Sal's new life. We learn about her parents, her strange relationship with the SymboGen CEO, and her super-amazing romance with the (of course) handsome, smart, and always-there-for-her Nathan Kim.

At times, Parasite feels less like a biotech thriller and more like a YA romance between a sensitive, extremely vulnerable Bella type and her amazing parasite doctor boyfriend. Sal is freaked out by everything, so every character (but especially the dashing parasitologist Dr. Kim) is always bending over backwards to take care of her, explain things to her, and make her feel less stressed out. To be fair, she is in a very real sense only six years old, and has been made a ward of her parents. Grant's representation of Sal's innocence is nevertheless grating sometimes, especially when Sal tells us over and over that she doesn't understand "sciencey" things, and wishes her boyfriend were there to explain them to her.

Luckily, this is just our first introduction to Sal — Parasite is the first novel in a trilogy, and we can assume she'll grow as a character over time. Grant has also built a fascinating world in this novel, along with an intriguing supporting cast. She's got a good ear for zinger dialogue, and you'll definitely rip though this novel in a haze of grossout excitement as the parasite menace spreads. There are evil mad doctors, semi-evil mad doctors, secret lairs, and a bunch of subversive revolutionary parasites.

Reader beware, though: Parasite ends on a cliffhanger, with nothing resolved, just as the action reaches a fever pitch.