This is one of the best books i have read in a while, but i will try not to gush too much. I will also try not to give too much away, since it is kind of a thriller/mystery novel.
The basic premise of Parasite is that in the not-so-distant future we are able to bioengineer custom organisms. Actually, we can do a little of that now, like that glow-in-the-dark pig.
So, in the world in this book a company named SymboGen create something called the Intestinal Bodyguard. The IB is an engineered tapeworm that lives in your guts and secretes useful chemicals. In the book, SymboGen cured diabetes by created an IB that secretes insulin at regular intervals, like a fully functioning pancreas would.
That's pretty cool, but personally i have a hard time believing that people would ever submit to this. Just look at all the hubbub created by GMO plants, which are often just cross breeds to make something more resistant to mold or whatever! FaceBook would be buzzing with conspiracy theories if anything like the IB was ever developed...
But a big part of reading sci-fi is the willful suspension of disbelief. That is where i had to take the leap. Your mileage may vary.
So, there are these modified tapeworms that get implanted into people. Our protagonist is one Sally Mitchell, who had a seizure while driving and slammed her car into a bus. Her IB eventually saved her, even though extensive brain damage made her have to re-learn her whole life.
The book follows Sal (she goes by Sal after being re-born after the accident) as she and her boyfriend, conveniently a parasitologist at a local hospital, deal with an outbreak of a disease where some people seem to be turning into zombies. And the zombies seem to know her somehow...
There is a lot more to the plot, including her boyfriend's long-lost mother, a violent psychotic who claims to be a tapeworm that has taken over its host, SymboGen possibly falsifying research, Sal's father (a military researcher) getting involved in dealing with the zombies... Oh, and a mysterious children's novel that seems to lead Sal and her boyfriend to something.
I don't feel like i can go much farther in describing this without giving anything away. I will say though that i was about 2/3 of the way through the book before i figured out what the big revelation would be at the end.
Grant does a really good job of keeping the plot moving. This book was a real page-turner, and i read all 512 pages in about 10 days. I really didn't want to put it down to do boring stuff, like work, etc.
This is supposedly the first book in a trilogy, and the ending certainly sets up the next book. I want to see where this goes.