Theo and Scott’s pack are still in their fight at the beginning of the episode. Parrish appears in his hellhound visage. All attempts at fighting him are seemingly ineffectual. During the cacophony Valack is able to steal Lydia and disappear down into the sewers. The packs remain with Parrish, trying to fight him off as he is in his hellhound trance. Theo throws a pipe into his chest as though he is some Olympic javelin thrower. Stiles goes after Lydia, Theo helping as he catches Lydia’s scent.
Scott and Liam search for Meredith, a fellow banshee, so she can help them to find Lydia. Meredith is largely catatonic when they find her in her cell at Eichen House. The only thing Scott can do is tap into her spinal cord and her memories so she can tell him how to find Lydia. Meredith knows Valack thinks that by amplifying Lydia’s power she can figure out who the Beast is. Only Parrish can find Lydia since he is a hellhound – another mystical creature whose powers are vague and convenient all the time.
Valack takes Lydia down to his creepy lab. She sees the nurse Valack murdered by putting the Dread Doctor helmet on her. He continues to try and amplify her power through weird science. If there is a reason why Lydia’s hair has been constantly wet for basically the entire season, it is unclear.
Scott and Liam find Parrish in a random stairwell where no one really knows how he got there or how he survived a pole to the chest from Olympian Theo.
Stiles gets the idea to break the sewer pipe so he can hear the sound of Lydia’s voice and find her. They are successful but just when Stiles and Theo find her, Lydia screams. It doesn’t kill them. Instead it opens the door and kills Valack who was about to put the Dread Doctor mask on her. Lydia is relieved that Stiles came back for her and they walk out together. Theo notices the Dread Doctor headgear in the corner.
Lucky for Hayden Tracy left some kamina venom behind. She uses it to paralyze Deucalion so she can leave and help her pack. Mason has been tasked with opening Eichen House back up. He almost rams the transformer with his car. Luckily Hayden comes upon him and jumps the wall. They are successful in opening up Eichen House so the pack can escape.
Parrish is able to burn the mountain ash out of the walls. He passes through the gate and Liam and Scott follow. Stiles is doing his best to help Lydia but her screams are overcoming her. Valack is dead but her life is still in danger. Luckily Parrish arrives just in time to contain her screams. Somehow he is impervious to her powers and is able to stop her from killing anyone else. More logic that has not been explained.
The pack is mostly reunited and they attempt to make their way out. Just in time for them to relax, Tracy attempts to kidnap Lydia for her chimera pack’s own purposes. But it is Lydia’s mother Natalia who saves them this time! Finally! They drive Lydia to the vet clinic, which seems like a strange place to treat a woman having a seizure. Deaton has the answers and shoots mistletoe into Lydia’s brain.
The windows explode and Lydia doesn’t get up. Stiles is the one constantly at her side. She is deathly pale and her face is covered in glass. Dylan O’Brien does everything without saying a word. Earlier in the episode when Stiles saves her Lydia says in awe “you came back.” These are two people so equal in intellect and their devotion to each other that it seems impossible they’re not together at this point in the show. Maybe they never will be but the look they share when Lydia wakes up is pure love.