3x02 - Chaos Rising
Derek and Isaac call Peter over to perform a mind meld. Derek doesn't know how to do it and doesn't want to hurt Isaac. They want to access Isaac's memories of where he found Boyd and Erica. The process is painful for Isaac, but they learn that Erica and Boyd are going to be killed the following night. Peter then sits back and watches as Derek, Stiles, and Scott plan a rescue attempt. He doesn't think the risk is worth it. After Derek and Scott leave, Peter snarks at Stiles while Stiles worries over the fact that Boyd and Erica have been kept for three months. Peter asks what the bank vault is made out of and Stiles reports that it's hecatolite. This means they haven't been changed by the moon in months, which will make them more rabid. They call Scott to tell him, but it's already too late.
3x03 - Fireflies
While Derek, Scott, and Isaac are out trying to catch Boyd and Cora, Peter shows up to give him a piece of his mind. Derek is contemplating killing Boyd and Cora to stop them from killing innocent people. Peter says that it was Deucalion's plan for Derek to have to kill them all along, so doing it now is just playing into his game. He advocates letting them kill a few innocent people if it means thwarting Duke.
3x05 - Frayed
After Scott discovers that Deucalion is living in Allison's building, he goes to Derek's loft to let them know, only to find Peter, Derek, and Cora planning a preemptive strike. Scott doesn't think killing everyone should be the answers, but Peter doesn't see a problem with it. Following the confrontation with the alpha pack that Derek's pack lost, Peter and Cora go to the abandoned mall to look for evidence. They then go to the Animal Clinic and find the entire alpha pack there. They see Kali come outside to roar in agony and Peter figures her sorrow isn't for Derek.
3x08 - Visionary
Stiles shows up at the loft asking about Derek being missing following Boyd's death. Cora tells him a story about Derek and Peter being out in the woods when hunters came. They hid in a root cellar for two days to escape them. The point of her story is that werewolves are taught to go to ground and hide when threatened. Peter comes down and tells them that the reason Derek is different from when Cora knew him is because of what happened to him as a teenager. He says that what changed Derek is what changed the color of his eyes. Peter explains that Derek fell in love with a girl named Paige. We are shown Peter following them around as they go to a private place to make out. Stiles asks how old Derek was and Peter is cryptic about werewolf ages. Because Peter followed them to the distillery he is there to witness the meeting of a few packs, led by Kali, Ennis, and Deucalion, who want to talk to Talia about the Argents. Ennis declares a blood feud over one of his betas. Peter tells them that the death of one of Ennis's betas meant an opportunity for Derek, although this is highly suspect. Peter claims that Derek was obsessing over Paige finding out he's a werewolf, but it's Peter who tells him that he can't be with her unless she's turned. He tells Stiles and Cora that he urged Derek not to have her turned, but in reality he was pressuring him into it. It's unclear who made the request of Ennis, but Derek tries to stop him in the end while Peter watches. The bite didn't take and Paige was dying a slow and extremely painful death. Derek took her to the nemeton and killed her out of mercy. Peter put her body where someone would find it. He explains that taking an innocent life turns a werewolf's eyes blue, although we later learn there is more to this explanation in Season 5.
3x10 - The Overlooked
Peter is at the hospital looking after Cora while everyone is evacuating. He calls for help, and it gets Melissa's attention. This is first she learns that he isn't dead. The twins show up and take Cora. Peter tries to fight them, but he's no match being as weak as he is. Derek and Scott take on the twins while Peter and Stiles slip by and pick Cora up. They all run for safety and stop to assess whether Cora is okay. Peter reports that she's only getting worse. Jennifer shows up and claims that only she can help. When Duke has Melissa call over the PA system that Jennifer needs to be delivered to him, Jennifer reveals that Duke would never hurt Scott's mom because he wants Scott in his pack because he's rare. Peter realizes that Scott is a True Alpha. They decide not to hand Jennifer over but still need a way to get past the twins to get Cora to the ambulance. Peter takes a shot of epinephrine, which gives him a strength boost. He and Scott distract the twins while Derek, Jennifer, and Cora escape. As the boost wears off, Peter can barely walk. He and Scott escape down a laundry chute. Scott delivers Peter to the ambulance where Stiles is waiting with Cora and then heads back to help Derek. When Isaac shows up with Chris's car, Stiles, Cora, and Peter transfer to that and get taken to the rally point.
3x11 - Alpha Pact
Peter disappears when he sees Chris and Allison coming toward the vehicle. He appears again when Derek brings Cora back to the loft. Isaac yells at Derek for being useless and leaves. Peter advises that he not take it personally because Isaac is planning to leave his pack for Scott's. Peter watches Derek continue to take Cora's pain and warns him to be careful. He says that an alpha can sacrifice their spark in order to heal someone. It's clear that Peter is goading Derek into giving up his alpha spark even as he warns him of the dangers. Not only could it kill him, he'll leave himself weak for when Kali attacks which will push him into Jennifer's arms. Later, Lydia shows up asking them about the location of the nemeton, but Peter explains that Talia took the memories of it from them. Derek decides to heal Cora in the end, sacrificing his alpha spark.
3x12 - Lunar Ellipse
After Derek heals Cora, Peter continues to gripe about how weak he's made himself. He seems genuinely concerned that Derek is going to be killed by Kali. When Ethan and Lydia show up to report that Kali and Aiden are coming to kill Derek, Peter urges Derek and Cora to leave town. He, himself, disappears until after the fighting is over. He finds Jennifer nearly dead near the nemeton and slashes her throat to make sure she stays dead this time, declaring, "I've always been the alpha!"
3x13 - Anchors
Derek and Peter are chained to a metal fence in a basement in Mexico being electrocuted. Derek glares at Peter and blames him for their situation. Peter grouses but admits that it is his fault they're being tortured.
3x14 - More Bad Than Good
The hunters question Peter and Derek about La Loba. They claim to not know anything. Peter calls the threats to cut them in half medieval, so the hunters threaten him with a chainsaw instead. Araya Calavera comes in and threatens them in a different way. She holds a knife to Peter's eye and asks him where La Loba is. When he doesn't tell her, she cuts off his finger. Peter asks them if they can put his severed finger on ice and requests a band-aid. Braeden then comes in and sets them free, even though she wasn't paid to get Peter. Peter grabs his finger. They head upstairs and find a mountain ash trunk filled with ashes. Only Braeden can get the triskele urn that's inside it.
3x15 - Galvanize
They return to Derek's loft where he sews Peter's finger back on. Peter asks for anesthetic, but Derek won't give him any. He opens the box and shows Peter that it contains Talia's claws. Peter thinks that's both touching and morbid. Peter doesn't understand what they're supposed to do with the claws until Derek starts placing them into finger holes in the urn. Derek explains that this is why he sewed his finger back on. Peter only agrees to do the mind meld using Talia's claws if he can have them afterward, "for sentimental value." Derek knows this is a lie but agrees. Peter jabs the claws into Derek's neck relishing the fact that it will hurt him quite a bit. Once the meld is over, Peter demands to know what Talia said about him. Derek just glares at him, which Peter interprets as nothing good.
3x19 - Letharia Vulpina
Peter goes to the high school to talk with Lydia's mom. He claims to be from the Health Department there to do hearing tests. After he's sure Lydia has noticed him, he leaves. This prompts her to come see him later, because she thinks it was a message about her powers. Peter greets Lydia and Allison in melodramatic fashion and tries to get Allison sent away. Lydia refuses. He claims that she owes him for having brought out her powers. Allison gets tired of his grandstanding and tries to make Lydia leave, so Peter offers her a piece of information. The scream lets her drown out everything else so she can hear. Hearing is her real talent. In return for his help, he wants her to retrieve the memory that Talia stole from him, which is locked inside the claws. Peter tries to get Lydia to focus but gets frustrated with her. His anger causes Allison to go on the defensive and the tension between them makes Lydia throw Talia's claws. When she does, she hears something. She informs Peter that he's not just an uncle. When he tries to demand more information, Allison tasers him and the girls leave.
3x22 - De-Void
Peter finds Derek in his loft studying the chessboard left by Stiles and expresses concern over Derek's shoulder not healing from one of the Oni's swords. Derek says that if the nogitsune thinks this is a game, he wants to figure out the nogitsune's plays. Peter explains the nogitsune has lived too long to play by human rules and that chess is Stiles' game, not the nogitsune's. Before he leaves, he tells Derek to put something on his wound so it doesn't get infected.
Scott, Deaton, and Lydia think that the only way to get rid of the nogitsune is to give Stiles the bite, but Scott doesn't know how. Lydia suggests they call Peter as Derek isn't answering. Peter doesn't think Stiles would survive in his weakened state, but he also doesn't think it's the only option. He advises going into Stiles' mind and pulling him to the surface. He's only willing to help in exchange for what Lydia knows about his kid. Peter positions Scott's claws on Stiles and Lydia and initiates the meld. While Lydia is under, she starts to bleed and Peter calls to her, telling her she's stronger than this and tells her to concentrate. He yells her name and his voice leads her where she needs to go, the white room with the nemeton. When they come out of the meld, Lydia tells him that his daughter's name is Malia. Then, when the nogitsune starts vomiting up bandages, Peter protectively pulls Lydia back and positions himself in front of her before helping to tackle the being that crawls out. He's shocked to find that it's Stiles.