Kendra is a smart, rational, careful girl with powers of light. Seth is a immature, rash, risk-taking and courageous boy with powers of darkness. Sibling Yin-Yang at its finest.
So what happened to Mrs Price, Kendra's home room teacher who was bitten by Vanessa and was controlled into attacking her students and the principal and fleeing the premise,never to be seen again?
Option 1: She woke up on the street somewhere, with her last clear memory of being in class, with no memory of how she had gotten there, no transportation and possibly no money or cellphone. If she manages to make it back, she'll find she's been fired for attacking several students, and most likely arrested or deemed mentally deranged. The worst part is she'll have no idea what happened to her and will be horrified over what she thinks she did.
Option 2: The society killed her.
Considering that's what they did with Rex in book 4, it seems the most likely option.
When you realize the Society killed Rex, an innocent daycare volunteer worker, simply because they couldn't afford to leave loose ends.
What happened to Aaron Stone? The last we ever hear from him is in Obsidian Waste when Trask says he'll contact him via radio to tell him to fly the helicopter away from the preserve to safety. We never learn of his fate. Did he safely escape, or was he killed and Zombified?
In The Grip of the Shadow Plague, Dougan appears to have no idea why Warren has been missing for several years. He said he thought that Warren had left the Knights. Warren's mission to secure the artifact was implied to be of critical importance and top secret. Dougan, having one of the highest positions in the Knights of Dawn, should have known of Warren's mission. Did the Knights of Dawn ever inquire as to why one of their top agents disappeared on an important mission? When Maddox went missing while scouting out the Brazilian preserve, Tanu went looking for him. Did anybody look for Warren? The Sphinx isn't one to leave loose ends, as Captain he would have looked into it.
On a similar note, how well did Dale, Stan and Ruth look into curing Warren's catonia? Dale says in The Rise of the Evening Star that Warren was on a mission for The Knights of Dawn, so they knew who had sent him. However, in The Grip of the Shadow Plague, Dougan doesn't have any knowledge as to why Warren had gone missing for so long. Wouldn't Warren's family have inquired into the Knights of Dawn as to what Warren had been doing that had turned him into a catonic albino? Even when Tanu, Coulter and Vanessa, who are all Knights, join the group, it never seems to occur to them to ask the Knights of Dawn. Warren's mission was implied to be top secret, but Trask states in Secrets of the Dragon Sanctuary that the Knights of Dawn have a special fund for collateral damage. Shouldn't they have at least helped with Warrens recovery? It's implied that the only people who knew of Warren's condition were people who lived on the preserve. This seems like a ridiculous oversight on someone's part. It is much easier to ask for a guaranteed assistance than it is to risk asking a Jinn and getting turned into a chicken.
I probably just missed something, but did it ever explain why the Society needed Olloch in the first place?