After several books, I think it's safe to say that genre-melding is the defining characteristic of the fiction Seanan McGuire writes under the "Mira Grant" pseudonym. Where McGuire's urban fantasy series (both the October Daye books and the InCryptid series) revel in exploring the tropes of that genre without reaching beyond its accepted borders, her Mira Grant books (the Newsflesh trilogy and now Parasitology) dance lightly across genre boundaries. The Newsflesh books weren’t just zombie tales: Feed (2010) was a political thriller à la All the President's Men, Deadline (2011) was a medical thriller that could have come straight from Robin Cook, and Blackout (2012) at times felt like a Tom Clancy action tale.

Parasite, the first book in a new duology, has all the trappings of a conspiracy thriller set against the backdrop of a not-so-distant future (the year 2027) in which the science is just sufficiently advanced from the present day to be fictional. Each section and chapter begins with quotes from the literature of the day: memoirs and technical papers of the scientists responsible for developing the titular parasite, news reports, articles analyzing the effectiveness of the ad campaign that introduced D. symbogenesus to the public. These present a convincing picture of just how such a parasite, intended to cure the average person of all medical ailments, could come to be. And isn't that what the best conspiracy thriller do? Convince us that the conspiracy is as real as the world outside our windows? Grant clearly enjoys doing her research and cobbling the future together out of the scientific advances of the present.

If there's anything McGuire/Grant loves more than research, however, I would guess it's writing strong female characters in the first person. In Parasite, that strong central female character is Sal Mitchell, a functional amnesiac, the first person to essentially come back to life from a should-have-been-fatal car accident thanks to the Symbogen Intestinal Bodyguard parasite in her bowels. In 2027, the majority of the population have safely had the parasite placed in their bodies and seen their medical woes washed away by the parasite's secretions, but no one had ever come back from the dead until Sally Mitchell ran her car head-long into a bus, was declared brain dead, and then woke up just before being pulled from life-support by her doctors and grieving family. The question of how Sally came back when no one else ever has is one of the underlying mysteries of the book, as is the question of whether the founders of SymboGen had any idea this side effect was a possibility.

Because she's the first, Sally is subject to as much media scrutiny as she is medical. The cost of returning to the living is amnesia; Sal, as she now prefers to be called, cannot remember what it was like being Sally, cannot remember anything from the time before reawakening. Six years after waking up, she has managed to build a new life (scientist boyfriend, animal shelter job, better ties with her sister) but is still very much a tabula rasa that SymboGen hold tight strings on. Sal being an amnesiac allows her to be the focal character and also the reader's way into this future world. When Grant wants the reader to understand a common, everyday facet of the world Sal lives in, she can have Sal ask someone for an info-dump without it feeling out of place. Sal is the one who feels watched, who feels SymboGen knows more about how she survived her accident than they are admitting, and so the sense of conspiracy builds easily around her. She's not drawn into someone else's wild theories, she is at the heart of her own. And when people around her start developing a "sleepwalking sickness," the conspiracy moves from possible to real and from "just about Sal" to something much bigger.

The descriptions of the sleepwalkers start out mild: they are slack-jawed, shambling, zombie-like (although to my memory no-one mentions the Z word in the book). It's not until halfway into the book that the vague sense of dread these descriptions evoke becomes something more solid. Sal's escort on the SymboGen campus, Chave, has gone slack-jawed and unmoving like the other sleepwalkers Sal has seen. SymboGen security responds in what Sal thinks is an extreme show of force, triggering her "conspiracy" thoughts. Sal starts to move away from her, but Chave moves suddenly to grab her by the throat, and Sal is forced to confront what she doesn't want to see:

It was like looking at a dead thing. The comparison had occurred to me before, but I hadn't realized how apt it was. There was no emotion in her eyes, no animation, nothing but the cloudy blankness of a body that has been abandoned. She was moving, her hands were doing their best to strangle the life out of my body, but Chave—the bitchy, efficient, focused woman who had been a fixture of my visits to SymboGen since the beginning—was no longer living there. (p. 143)

From that point on, we know, as Sal does, that the danger is real and there is clearly a conspiracy going on, one that involves the highest levels of SymboGen, possibly the government (Sal's father is a high-ranking USAMRIID official and also has some secrets he's keeping), and possibly a mysterious scientist that Sal and her boyfriend are drawn to through the pages of an eerie children's book, Don't Go Out Alone, whose rhymes and motifs are repeated throughout Parasite. It takes, as I said, almost half the book to get to this point but the slow build of tension through Sal's first-person narration, her confusion as to what is real and what is her own amnesia-inspired paranoia, makes the wait worthwhile.

Unfortunately, the slow build doesn't burst to a boil even at this point. More layers are added, more disturbing encounters (with sleepwalkers and with other odd characters) are heaped on to fray Sal's, and the reader’s, nerves to the breaking point . . . and then the book ends with a cliffhanger that leaves the major character arcs and main plot unresolved. This is by design—Parasitology is a duology, well-advertised as such—but the lack of closure bothered me more than I thought it would going in. Grant's strong point in the Newsflesh books was that each of its installments was a complete book with a main story that is satisfactorily resolved while still leaving questions and threats to be answered in the next book; Parasite ends on a frustrating note for anyone who has become fully invested in Sal and her friends. On the one hand, kudos to Mira Grant for writing characters I'd really come to care about over the course of five hundred pages. On the other, curse you for making me wait for the next five hundred.

Part conspiracy thriller, part science fiction, part horror, and part character study: in Parasite, Mira Grant strives to provide something for everyone, and pretty well succeeds. Except for those of us who want all the answers right now: did I mention I’m not thrilled about having to wait a whole year for the concluding half of this story?

Anthony R. Cardno's reviews have also appeared in Icarus and Chelsea Station. His short fiction can be found upcoming in Beyond the Sun (Fairwood Press) and Oomph (Crossed Genres). He interviews creative types at www.anthonycardno.com and can be found on Twitter as @talekyn.