Lydia and Allison hang out and talk after Allison gets back from France. They are both supposed to be moving on from their previous boyfriends. It so happens that Scott and Stiles are on the same stretch of road, and they see one another. Lydia hurries to get away, but stops when she sees that Stiles has stopped. Her car gets hit by a deer. At school, she and Allison encounter Braeden, who leaves matching marks on their arms.
They go to find Scott to show him the marks, and Scott arranges a meeting with Derek to see what he thinks it means. Derek is unimpressed and still blames Lydia for drugging him and resurrecting Peter. While Allison continues to research the symbol, Lydia takes note of Ethan and Aiden and claims she wants the straight one. Allison leaves when she figures out where the symbol is from, and Lydia goes home. That night, she screams although she doesn't know why.
Lydia tries to go to the store but ends up an a public pool, unsure how she got there. She finds a dead lifeguard with a purity ring and calls Stiles. He takes note of the ring and brings her home.
Stiles comes to Lydia with his theory that the human sacrifices are virgin sacrifices. He also tells her that Aiden is an alpha, which she didn't know. She discourages him from trying to figure everything out on his own, though. Later, Lydia is in the music room drawing a picture of a tree. Danny compliments her on it but wonders why she's in the music room since she doesn't play. She finds a recording that suggests that the music teacher has been taken as a sacrifice. She calls Stiles, and he brings Deaton to the school. They figure out that the new set of people being taken are soldiers and that the culprit is a darach.
Lydia and Allison follow the cross-country team to their meet. Allison accuses Lydia of hooking up with Aiden, and Lydia denies it although it's true. When Stiles calls, Lydia pretends that she and Allison are at a movie, but Stiles knows they've been following them. He tells them Scott's in trouble. When they get the bus to stop and get Scott into a bathroom, Lydia explains that Scott isn't letting himself heal. After they stitch him up, Lydia and Stiles discuss the darach.
The cross-country team stops for the night at Motel Glen Capri. Lydia gets a very bad feeling about the place, though. She goes to the front desk to get towls and notices a counter showing the number of suicides. She hears people through the vents talking about killing themselves and hears the shots. But when they go to look, the room is empty. Lydia wants to leave. When they go to the front desk, she sees that the suicide count has gone up and realizes that people are about to kill themselves.
They hear Ethan about to cut himself open with a saw, and Lydia pulls the plug. They find Boyd drowning himself, and Lydia remembers that there are flares on the bus, which Stiles can use to snap Boyd out of his trance. She also finds Isaac hiding under his bed. Stiles, Lydia, and Allison find Scott in the parking lot, having doused himself with gas. He has a flare in his hand. Stiles stops him and throws the flare away. Lydia sees the flare roll back toward the gas and tackles them all out of the way. She sees the darach in the ensuing flames. The next morning, Lydia figures out that Coach's whistle has wolfsbane in it, which is what made the werewolves go crazy.
Lydia and Aiden are making out in Coach's office then the fire alarm goes off. Cora warns Lydia to stop dating Aiden, but Lydia thinks she has everything handled. Cora starts to threaten her, but Stiles shows up needing Lydia's help to find Deaton. He has Lydia try a Ouija board first, but she doesn't come up with anything. They try psychometry and automatic writing. Stiles gets exasperated with her. She comments that they're talking to the wrong person. They should be talking to Danny since he was a target but not a sacrifice.
Together, they go to the hospital to dig through Danny's things, then head to the clinic. There, they combine the telluric currents map with Chris Argent's map of sacrifices. The group splits up, and Lydia, Stiles, and Cora go to Derek's loft, where he's fighting Kali. They turn on the power, electrocuting Kali, Derek, and Boyd, and arrive at the loft in time to see Boyd dead.
Lydia is already at the school when Scott and Stiles arrive. She explains that it happened again, where she tried to drive somewhere and ended up in another location, this time the school. They find Deputy Tara Graeme dead on the high school sign. During class, Scott and Stiles want to talk to Ethan, so they get Lydia to distract Aiden by having sex in the Coach's office. He's skeptical that she wants him all of a sudden, since she hasn't talked to him since they killed Boyd. They talk about the hierarchy of the alpha pack. Cora comes to break them up, and she and Aiden fight.
Later, Lydia walks by the history classroom and sees a piece of chalk roll across the floor. She finds a five-fold knot written on the blackboard and knows that another teacher has been taken. Lydia sounds the alarm, but no one believes her. That night she goes to the recital and gets a text from Aiden telling her to meet him in a classroom. Ms. Blake attacks her there and ties her to a chair. She tries to strangle Lydia, but Lydia gets her hand under the garrote and screams. Jennifer realizes that Lydia is a banshee, and all the Werewolf hear Lydia's scream. The Sheriff arrives and keeps Jennifer from killing Lydia but gets taken as a sacrifice himself.
Lydia and her mother talk about the bruising on her throat from the garrote. Her mother suggests she cover it up with makeup, but Lydia doesn't think she has anything to hide. Stiles shows up and tells her that Scott has gone over to Deucalion's side. Lydia doesn't believe it. She also doesn't know why Jennifer tried to kill her, since it wasn't because of her banshee powers. While they're at school, Stiles starts to have a panic attack. Lydia pulls him aside and kisses him to make the attack stop. She suggests he see a guidance counselor, and they go to talk to Morrell about the darach.
Stiles starts looking through the files on everyone and finds Lydia's file. It's full of her tree drawing. He realizes that her drawing is always the same. Stiles recognizes it as a drawing of the nemeton, but they don't know where that is. He sends Lydia to talk to Peter and Derek about the root cellar. She goes, but Peter claims Talia took their memories of the root cellar, so they don't know where it is. Everyone gathers at the Animal Clinic where Deaton broaches his plan to sacrifice Scott, Stiles, and Allison to find the nemeton. When they perform the sacrifice, they need a tether to hold them to life. Lydia goes with Stiles.
Lydia, Isaac, and Deaton wait 16 hours for the Scott, Stiles, and Allison to come back. Ethan comes to the clinic looking for Lydia because he needs her help in stopping Aiden from killing Derek. They go to the loft to tell Derek and Kali and Aiden are coming, but he isn't convinced to leave until Lydia says that she feels like she's standing in a graveyard. Lydia and Ethan stay behind to meet Kali and Aiden when they arrive. Jennifer shows up and kills Kali and the twins, then threatens Lydia until she screams. The scream makes Derek and Cora turn around and come back. Jennifer tempts Derek into joining her while Lydia and Cora watch.
When they leave, Lydia and Cora take the twins to the Animal Clinic because they aren't quite dead. Aiden is pleased to find that Lydia cares about him, although she pretends not to when they're back at school.
In Stiles's dreams, Lydia is lying next to him in bed as he wakes up from a nightmare. She tries to comfort him and gets upset when he goes to open up a door in his room.
The real Lydia runs into Allison at school, after Allison finds herself in the hallway at the end of a nightmare vision. Scott and Stiles meet up with them, and Lydia is thrilled to find out that they're all having weird problems and she isn't the only crazy one. She tries to help Allison with her problems, both in art class and out in the woods with her archery. Allison's hand is too unsteady to shoot properly. When Allison starts having a vision, she almost shoots Lydia in the face, but Isaac is there to catch the arrow.
When Scott needs to learn how to use his alpha powers, they ask Lydia if she can get the twins to teach him. They all meet at the loft, where the twins beat the hell out of Scott without him learning to roar. Lydia accompanies everyone to the preserve on a the hunt for Malia Tate. She steps on a leg trap and has to talk Stiles through disarming the trap before it clamps down on her leg. He does it, and they cling to each other in relief.
During class, Lydia keep waving her hand around like she's swatting flies, even though there don't appear to be any flies. Aiden goes to see her, and while she initially tells him that they're not going to date, they end up making out in the guidance counselor's office. When they learn that William Barrow is on the loose, Lydia insists that he must still be at the school because the buzzing she's been hearing keeps getting louder. Everyone starts looking for Barrow. Lydia and Stiles go to the art room where they see a picture of an explosion and realize that someone like Barrow could blow up the school. They pull the fire alarm to get everyone out.
Stiles and Lydia go back to his house. She apologizes to him for getting him in trouble, but he insists that he believes her. They head back to the school and look in the chemistry lab closet and find evidence that Barrow was there. They also find atomic numbers that spell out Kira's name and know who Barrow's next victim is. They are too late to save Kira from being taken. Lydia says that she wants to scream, so Stiles encourages her to. When she screams, she realizes the buzzing she's been hearing sounds like electricity. This leads them to the power station.
In class the next day, Aiden talks to Lydia. She doesnt' want to date him because he's a bad guy. Aiden offers Derek's loft to Danny as a place to hold his black light party in part to impress Lydia and show that he can be helpful. At the party, Lydia is by herself observing everyone else. She shuts Aiden down and just watches. She gets the sense that something is wrong and starts looking for Scott. She rushes outside and encounters Oni but gets silenced before she can scream. Danny and Aiden later find her passed out. They rush her inside, and Aiden holds her near a heater to warm her up.
When the Oni attack inside the party, Aiden has Danny get Lydia out of there.
Lydia and Aiden are at the school late a night so she can draw him. He was thinking this would be nude modeling and starts to undress, but Lydia gets distracted by a voice coming over the radio. She hears Stiles begging for help. She and Aiden go directly to Stiles's room and find that his murder board has been rearranged so all the red strings are tried to a pair of scissors stabbed into the middle of his bed. Scott and Isaac show up so they can get Stiles's scent to go looking for him. Lydia insists on telling the Sheriff that Stiles is missing. While Scott and Isaac leave to start looking, Lydia and Aiden stay to look for clues. Aiden plucks one of the strings, which causes whispers that only Lydia can hear. She believes him to be in Eichen House.
Lydia, the Sheriff, and Scott go to Eichen House. She's positive that he's there, but then they go into the basement, it's empty. The Sheriff gets upset, and Lydia feels terrible for being wrong, even though in his own head Stiles is in the Eichen House basement. After Melissa and Agent McCall find Stiles, Lydia waits with everyone in the hospital to see if he's okay. She starts to mistrust her powers because they led her the wrong way. The whole day at school, she hears everything too loudly and runs to get away. She locks herself in her car and screams to drown everything out.
Lydia is at school and sees her mother talking to Peter Hale. Her mother is pleased that she got Peter's number, but Lydia knows something is wrong. She gets Allison, and the two of them go to see what Peter wanted. Peter wants Allison to leave, but Lydia isn't having that. Peter wants to make a deal. He'll help Lydia with her powers if she will help unlock his memories trapped in Talia's claws. Peter explains that Lydia's hearing is attuned to a level of the universe that no one else can hear and her scream is a way to quiet everything else down so she can hear what she needs to. Allison and Peter start fighting with each other, and when Lydia gets frustrated, she throws Talia's claws. They make a sound when they hit a post that tells Lydia Peter has a daughter: Malia Tate. She refuses to give Peter the name, though. He thretens her, and Allison takes him down with her taser.
Allison figures out that the shugendo scroll which is supposed to tell them how to stop the nogitsune is in Katashi's silver finger prosthetic. This piece of evidence is going to be transported from the sheriff station to a federal lockup. Lydia has put together a plan to rob the armored truck that will be transporting the evidence. Ethan and Aiden join Allison, Lydia, and Scott to hear this plan. They want to put a GPS tracker on the truck and then stage an accident in front of it when it gets to Roosevelt Bridge. While the driver is distracted, they'll break into the back and steal what they need. Kira joins the plan last minute.
The actual plan goes awry when Kincaid shows up at the truck first. Lydia can't participate in the fight, so she waits in the background.
Lydia and Aiden are going to see Malia Tate. Lydia follows the directions from her GPS, only Aiden points out the GPS isn't on. The directions take them to a parking lot where they find Stiles passed out. They take him to Scott's house, where Deaton doses him with kanima venom. Lydia argues that Scott should give Stiles the Bite to change his body, which is supposed to expel the nogitsune. Scott doesn't want to and doesn't know how, so they call Peter. Peter suggests going into Stiles's mind and try to break him of the nogitsune's hold from inside. The terms of Peter's help are that Lydia will tell him his child's name. She agrees.
Lydia goes into the mind meld with Scott. They wake up tied down and Lydia reminds Scott that he's a Werewolf and can break out. They get separated, and Lydia gets lost in the memory of the night she was bitten. She gets scared and starts to bleed in the real world. Peter rushes to her and calls her name. When she hears him, she starts to run and bursts into the white room. Scott meets her there, and they can see Stiles and the nogitsune playing Go on the nemeton. They can't run closer, so Lydia advises Scott to howl to Stiles as part of his pack. The howling works, and the nogitsune starts to expel Stiles. While everyone is dealing with Stiles crawling out of the floor, the nogitsune kidnaps Lydia.
The nogistune takes Lydia to the Oak Creek camp. She can hear the echoes of the people who died there. She runs from the nogitsune, who is content to follow her around and scare her. She asks him what he wants and he tells her that his hunger for pain and chaos is insatiable. As they wait for nightfall, Lydia realizes the nogitsune is nervous. He is, but that's why he's keeping her close, so he will know when his death was drawing close. When the Oni appear, the nogitsune breaks Noshiko's last Tails and takes control of them. The Oni start fighting with Allison, Kira, and Issac, while Scott and Stiles find Lydia. She's angry at them for coming because she left a message telling them not to.
As they run to escape Oak Creek, Stiles stumbles and falls. Lydia stays with him. The moment Allison is stabbed, Lydia screams her name and collapses into tears.
Lydia, Scott, and Isaac sit in the sheriff's office answering questions about Allison's death. Afterward, Lydia and Scott go to the Animal Clinic to talk to Deaton. They tell him that the nemeton used to keep the nogitsune trapped, and he suggests that a box made of nemeton wood could do the same thing. Lydia suggests using the triskele urn that houses Talia's claws. They ask Derek to bring it to the school. Scott, Stiles, Kira, and Lydia go to the school to enact their final plan. Lydia holds Stiles up because he's too weak to walk on his own.
When they go in the school, they end up in an illusion created by the nogitsune. Lydia and Stiles draw closer as the nogitsune tries to get him to commit suicide. She stops him from stabbing himself in the stomach by suggesting it will be a trick. Stiles sees that it's an illusion and they are able to escape. As the nogitsune stalks toward them, they remind him about the scroll which says that he can't be a fox and a wolf. Scott gives the nogitsune the Bite, and Kira stabs him. Stiles passes out. When he comes to, Lydia gets the sense that someone else is dying. She runs outside to see Aiden die in Ethan's arms and turns to Stiles for comfort.
Later, Lydia sees Malia on her first day of school and gives her a sad smile.