As the conflicts of Parasyte continue to develop, Shinichi stops every now and then to ponder his humanity (or lack thereof). Sometimes he even discusses it with Migi, his appropriately named right-hand friend. But fictional tales are rarely the best place for intense intellectual examination, and Hitoshi Iwaaki seems to know it too, letting suspense and action guide the story rather than lectures in ethics and anthropology. The result is a string of story arcs that ebb and flow, sometimes thrilling, sometimes not-so-thrilling, but always moving with the kind of tension that can only be had when you're the one teenage kid on earth who can stop everyone else from being eaten by creepy-crawlies.

Most of Volume 4 involves Kana, the "parasite-sensing" girl that Shinichi met a few chapters earlier—another unusual character in his string of encounters. As the intentionally over-the-top dream sequence in the first chapter proves, Kana is very much a true idealist, too naïve to fight on the side of the good guys or the bad guys. Her presence is enough to set off a love triangle between her, Shin and his girlfriend, but frankly, this is not the kind of storytelling that Iwaaki is best at, and this plotline drags along until the dramatic, action-packed confrontation where Shinichi must come to Kana's rescue.

The next person Shinichi runs into, a private detective, makes better use of suspense—after all, what other way is there to feel when one is being followed?—yet it is the character's own softness that also hinders this part of the series. If the detective were more intellectually and emotionally capable, he'd probably be a good candidate for a classic game of cat-and-mouse, but instead, he's an easily manipulated weakling whose claim to fame is being the only person in the world to photograph one of the creatures ... before running off in fear. It seems even Iwaaki knew that this storyline wasn't getting him anywhere, and cuts it off briskly after the snoop gets a little too inquisitive.

The majority of Volume 5, then, takes on the much more fascinating storyline that's been bubbling under the surface for a while now: the creatures are starting to congregate. Now this is the suspense and action that drives the series at its best—Shin angers the wrong people, finds himself impossibly overmatched, and must fight for his life. There's even time to engage in some philosophy at this point, as Migi observes that the parasites must have developed a societal system after realizing that picking off humans one by one was painfully inefficient. So now they're not only frighteningly superpowered, but they're getting smarter?! That's exactly the kind of momentum that will help propel the series in chapters to come.

As the storylines move through various genres and themes, it's the artwork that most accurately reflects the creative energy being directed toward each segment. Some, like the Kana story arc, are rather lackluster (wacky dream sequence and climactic fight scene notwithstanding), relying far too much on straight-ahead paneling and talking heads for the many dialogue scenes. The private investigator storyline, too, lacks visual interest aside from the occasional chase or confrontation. But when the enemy finally starts teaming up against Shinichi and hunting him down, the artistic genius awakens at last: an intense chase scene spanning across city, town and country, an opponent whose morphing ability stretches the limits of imagination, and the kind of high-speed, split-second battles that grab the reader and refuse to let go. As always, it's Iwaaki's creature designs and sense of theatrics that steal the show, although it's a shame that the more fundamental areas—like human character design and backgrounds—always come out rather plain.

Also rather plain is the writing style, which works both for and against the series: it's nice to have a sci-fi/horror/action saga minus the melodrama and gobbledygook, but too much "straight talk" and things start to sound repetitive. Shinichi and Migi's high-minded discussions on the nature of humans, monsters, life and death can be refreshingly candid ... until one realizes that it's mostly the same stuff they've been saying since Volume 1, only worded differently. But if simplicity and readability are the goal, then this translation succeeds on that front (except for one typo), as well as adding occasional cultural footnotes on modern Japanese life. The author's replies to letters from the readers also provide insight into the creative process that one doesn't normally find in a manga compilation.

While Parasyte occasionally drags its feet through some of the story arcs, it is never outwardly bad; it simply prefers to lie in wait and pounce at the opportune moment. But even the lying-in-wait parts serve as part of the overall plan: the deliberate, almost dull pacing at these times ultimately magnifies the rapid-fire action scenes that follow later. Throw in a bit of dramatic tension, some philosophical reflections on humanity, and it's clear that slow buildup and frenetic climax are both essential elements of this series. Of course, the buildup isn't always executed perfectly—it can take some real patience to sit through pages of blandly drawn people discussing how to watch out for alien predators. But when those alien predators finally show up—well, prepare to be invaded by the ultimate thrill ride.