In MTV's latest episode of "Teen Wolf," no one is safe. A new infection that has been weaponized, the namesake of the episode, is released onto Beacon Hills high school. It is only fatal to werewolves.

A newly-introduced assassin and the biowarfare's manufacturer, an unnamed scientist, poses as a proctor for the student's PSAT. However, as the testing gets underway, more and more students begin feeling ill.

Meanwhile, the handy and resourceful Deacon is visited by another wolf pack leader, Satomi, with the same sickness killing off her entire group. Derek Hale (Tyler Hoechlin) also rescues Braeden, who was caught up in Satomi's pack when the virus was unleashed. Satomi describes the symptoms as extreme fatigue, werewolves lose control of transforming and eventual blindness before succumbing.

The school is quarantined and the Center for Disease Control is called to try and contain the sickness. Scott McCall and the other supernatural teens, all feeling the effects of the disease, try to sneak out of the school through a secret tunnel Derek told them about to avoid being identified as werewolves.

While it is too late for Satomi's wolves, she seems unfazed by the airborne infection. Between them, Melissa McCall, Derek, Deacon and Braeden are able to identify that Satomi was inoculated from a tea that she regularly drank, and there was more of the antidote in the Hales' vault.

In the previous season, it was alluded to that Malia, the most recent addition to the pack, might be the daughter of Peter Hale. However, none of her friends tell her this secret to protect her from seeking him out. When they find the Hales' vault, Malia is able to open it when the others can't.

Once inside, everyone except Stiles grows too weak to go further so he volunteers to go back and look for anything that might help. He reaches the school room and is confronted by the scientist, who threatens to kill him if he doesn't give up his friends.

At the last moment, Rafe McCall kills the assassin and explains to Stiles where to find the antidote to give to the others. Stiles races to them, and while he can't get back into the vault, he describes to Scott where the tea remedy is before they all become too sick.

In the final moments of the episode, Malia finds the dead pool list and, crying, storms out of the room.

"Teen Wolf" airs Mondays at 10/9c on MTV.

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