Darach

The Darach is an unknown character that has unknown intentions and is present in the third season.

Season 3
Throughout the first few episode in season 3, there are many mysterious attacks that Stiles is trying to piece together. The first attach occurs in Tattoo, where a deer runs straight into Lydia's car and shateering the windshield. The second time is mentioned when Lydia is telling Stiles about how her dog had bitten her, which is unusual. Stiles suspects an earthquake, as many animals do strange things when an earthquake is coming. Lydia brings up the rule of threes, which is that bad things happen in groups of threes. As she beggins to count them off, a large flock of birds come crashing towards the classroom window, shattering the glass and pecking at students, crashing into walls and dying. This is the third animal attack and little do the folk of Beacon Hills know, this is the doing of a Darach.

In Chaos Rising, Stiles friend Heather goes missing after he leaves her alone for a few minutes, which is seemingly suspicious. In the third episode of the third season, Caitlin and her girlfriend Emily are in a tent at the preserve, about to sleep together for the first time. They begin to kiss and caress eachother, but Emily freaks out when she finds a bug on her shoulder and all over the outside of the tent. In panic, she runs out of the tent and trips in the woods. Suddenly she is being covered by a carpet of bugs and she lets out a scream, when Kaitlin rushes out to find her she is gone. Later in the episode Emily is found tied to a tree by the neck, suffocated and left with a massive blow in the head. Lydia mysteriously finds a lifegaurd at night in similar situation, and calls for Stiles to help and the body is brought to the hospital. Melissa McCall explains to Stiles the injuries at the hospital, and shows him the exact same marks on a girl covered by a sheet who is revealed to be Heather. Stiles realizes that all three death victims were virgins, and that the kind of attack was called the three fold death.

In Unleashed, a high school senior named Kyle is killed in the same fashion after disappearing outside Deaton 's clinic, mentioning he was from a military family. But, when Stiles asks the victim's girlfriend if he was a virgin, the answer is surprisingly no, changing his perspective on the pattern of the deaths. He concludes that the deaths must be following the rule of threes, and that if the the first three were all virgins the next three will be something different. Seeking Deaton for help, he explains that all the evidence found points directly at the "Druids," an ancient religious class about which little is known but much is imagined and speculated. Deaton says the killer is NOT a druid, but somebody simply copying the centuries old practices of a people who should have known better. Lydia finds an audio recording on a phone in the music room, and when she plays it she hears someone playing the piano but abruptly stopping, hearing a chant (that we, the audience have heard in the background of all the murders) and a sudden scream. She calls Stiles and he comes over with Deaton, who says that every grouping of three would have their own purpose; virgins, healers, philosophers and warriors. Stiles asks if warriors could also be pertraining to soldiers, in which he responds yes. Stiles finds a picture of the music teacher wearing a military suit and points out that Kyle was in the Junior ROTC with Boyd, and that Boyd could be the third victim. Lydia interrupts saying that she thought of somebody else also with a military background, Mr. Harris. He is shown in his classroom grading papers when the chanting begins, he disapears. When Deaton and Stiles go look at his office for evidence, the papers have the letters "D," "A," "R," "A," "C," and  "H" on them, which Deaton explains is a "Dark Oak," or a Druid that went down the wrong path.