It premiered on July 10, 2021.
At Hexside, Luz finds Gus in the hallway upset because he messed up after trying to help Willow with a pixie problem. He used illusions to try and distract them, but he accidentally caused the pixies to attack Willow instead. Because of this, Gus has lost all confidence regarding his ability to perform illusion magic, and feels he should try something different. Luz assures him that he will feel better tomorrow, but when the next day comes, he feels even worse.
After receiving a message from Willow to tell him to stop sending illusion messages to her, Luz comes over to Gus' house for help, as she needs to use his library card to look up the human who lived on the Isles, as well as visit Amity. Along the way, Luz explains that she wants to go to the library because Eda's mother told her she might find a clue there. However, Gus expresses his feelings of inferiority, as he feels illusion magic just isn't as useful as other magic. Just then, they witness a Slitherbeast rampaging through the town. It almost attacks Braxus when three Glandus High students, named Bria, Gavin, and Angmar, intervene and help capture the beast. Gus is so amazed by them that he goes up to talk to them. Mattholomule then shows up with a map for the Glandus High students, leading to artifacts called the Galdorstones. According to them, they are powerful relics protected by a guardian in a place called the Looking Glass Ruins. Many witches have sought for them, but all returned empty-handed. Bria, Gavin, and Angmar are planning to seek out the stones with Mattholomule, and Bria asks Gus to join them, as they could need the extra help. At first, he turns down the offer, as he does not know any spells besides illusions, but Luz manages to encourage him, supplying him with some of her glyph cards to help him out.
While Gus is out on an adventure with the Glandus High students, Luz goes to the library. There, she discovers the name of the human was Philip Wittebane, and that he donated his diary to the library. Luz finds Amity, who is now an employee at the library, but is too flustered to approach her, as she watches Amity tying her hair up. Luz is then approached by Edric and Emira, who are there to look up skincare tips for Edric, as he has a date. Amity then walks up to Luz and, sensing something between them, Emira leads Edric off. Luz explains the situation and asks for her help in finding the diary. Amity tells Luz that a book that old would be kept in the Forbidden Stacks. Unfortunately, only Malphas, the master librarian, is allowed in. Amity agrees to help Luz out, but makes her promise to listen to her, as she could lose her job if they are caught being bad.
Meanwhile, Gus, Mattholomule, and the Glandus High students are in the Forearm Forest searching for the Galdorstones. Gus asks what the Galdorstones actually do, to which Mattholomule explains they have the ability to boost a witch's power, unless you're an illusionist. The Glandus High students have big plans for the stones: Angmar wants to grow an entire forest to create a butterfly sanctuary, Gavin wants to create the biggest abomination to impress his father, and Bria hopes to make life at Glandus High a lot better, as the weak students are pushed around by the strong. The kids arrive at their first challenge, which is a huge wall of thorns blocking their path. All of them encourage Gus to clear the path, so he feigns a fireball spell using a fire glyph, which blast a tunnel through the wall. While the Glandus High students are impressed, Mattholomule grows suspicious of it.
Back at the library, Luz and Amity are searching for Philip Wittebane's diary, while at the same time hiding from Malphas. Amity tells Luz that Malphas gave Amity her job at the library and her own study room. According to her, he is usually nice, but he would feed them to the bookworms if they got caught. Luz jokes that, even though they might be an unholy blood sucking snake monster in the Isles, in the human realm that word is usually a nickname for nerds. Amity says that the human realm sounds odd, to which Luz brings up the idea of showing it to her one day, which fuels Amity's resolve to help Luz even more. Not wanting to get her into trouble, Luz suggests they should head back, but Amity insists on finding the diary.
They eventually make it to the ruins, where they discover decrepit statues containing the Galdorstones. However, Gus discovers the ruins are actually a cemetery for illusionists, and the stones belonged to them. Gus says they should not take the stones, but the Glandus High students pay him no heed, as the illusionists are dead now, and they wouldn't have used the stones to their full potential anyway, being illusionists. Suddenly, the guardian appears, and Bria shoves Gus out to fight it. Gus realizes he is out of glyphs, so he creates an illusion of the guardian to scare it away, only to discover it too is also an illusion, and the caster is an old man who is the keeper of the graveyard. The keeper explains that illusionists like him have been guarding the stones for years, as they are the least likely to steal them, due to getting no power boost from them. Realizing the guardian is a fake, the Glandus High students restrain Gus and the keeper while they loot the Galdorstones. After being treated badly by them, Mattholomule helps free Gus and the keeper, as Gus saved him from detention despite the fact he was a jerk to him, while Bria has always treated him like a stooge.
After a long time searching, Luz and Amity find Philip Wittebane's diary, only to discover the pages have been eaten by a mouse. Luz cannot hold in her anger and shouts at it, alerting Malphas. Disappointed, he kicks the two of them out and fires Amity. Luz tries to apologize, but Amity is not up for it at the moment. She tearfully confesses that things are different ever since Luz showed up, and that she's always doing stupid things for her that she wishes she didn't do. To her surprise, Luz, also in tears, assures her it's alright, as she does stupid things around Amity too. Overwhelmed by all the information, Amity dejectedly heads home. However, Luz is determined to make things right and heads back into the library.
As Bria comes up with a plan to sell the smaller stones to the Emperor's Coven and keep the larger ones, Gus casts an illusion spell on the entire ruins. He lures Angmar with a butterfly, creates a poor depiction of Gavin's dad who wants to hang out with him (which tricks him despite his suspicions), and scares Bria away with horrifying images of the statues coming to life. With the threat gone, Gus cancels the illusion, which has tired him out. The keeper muses that perhaps it's time to hide the ruins forever, but Gus and Mattholomule beg him not to, offering to come by regularly to help rebuild it, which the keeper agrees to. Gus then asks Mattholomule if this means that the two of them are friends now, which Mattholomule confesses he doesn't know. As they are leaving, Mattholomule calls Gus "squirt" and punches him jokingly on the shoulder, to which Gus calls him "jerk" and jokingly punches him back on the shoulder.
Back at Blight Manor, Amity confides in Emira as her sister brushes her hair, telling her about how confusing Luz's arrival has made everything, and how she is feeling and thinking things that she never has before. Emira questions why she is making it sound like a bad thing, as Amity wasn't happy before. Emira then points out that Amity's roots are growing out, and asks if she wants to dye her hair again. However, Amity requests to have it dyed lilac purple instead. Luz then arrives at Blight Manor, beaten and bruised with Amity's staff card, apologizing profusely for what happened, but is shocked by Amity's new look. Amity explains that she felt like it was time for a change, and the two blush. Amity asks how she got the card back, and Luz explains that, after going through a series of harsh trials, she was able to convince Malphas to give her job back.
Amity then notices that the mouse that ate the diary had hitched a ride on Luz's leg. Luz declares she hates the mouse, but Amity informs her that it is an Echo Mouse, which can consume knowledge through eating things and can play back anything it eats. Amity then pets the mouse, causing it to play the first entry of Philip Wittebane's diary, which talks about how he ended up on the Boiling Isles and how he resolved to return home. Realizing she can still learn about Philip Wittebane through the mouse, Luz decides to keep it, saying that she hopes they become "good friends". Amity is so moved by what Luz did for her that she tells her that she always has a way of sneaking into people's hearts, before kissing Luz on the cheek. Luz's eyes light up in wonder, while Amity runs back inside her house, completely flustered, leaving Luz collapsed on the ground, still in shock about what just happened.
- Sarah-Nicole Robles as Luz Noceda
- Alex Hirsch as King
- Issac Ryan Brown as Gus Porter
- Mae Whitman as Amity Blight
- Tati Gabrielle as Willow Park
- Erica Lindbeck as Emira Blight
- Ryan O'Flanagan as Edric Blight
- Jorge Diaz as Mattholomule
- Felicia Day as Bria
- Nik Dodani as Gavin
- Harvey Guillén as Angmar
- Roger Craig Smith as Warden Wrath
- Fred Tatasciore as Malphas
- Kevin Locarro as Braxas
- Alex Lawther as Philip Wittebane
- Dee Bradley Baker as Guardian and Gavin's Dad
- Erica Lindbeck as Green Hexside Girl
- Eden Riegel as Pink Butterfly Illusion
- Christopher Swindle as The Keeper
- Fred Tatasciore as Slitherbeast
- Kari Wahlgren as Blonde Hexside Kid
Title in other languages
|Spanish (Latin America)||A Través de las Ruinas del Espejo||Through the Mirror Ruins|
|Portuguese (Brazil)||Trilhando Através das Ruínas||Treading through the Ruins|
|French||Les ruines de l'illusion||The ruins of illusion|
|For a full transcript of "Through the Looking Glass Ruins", click here.|
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- The secret message, found on the base of a statue in the Forbidden Stacks, translates to "strings".
- This is the first episode where neither Eda nor King physically appear, making Luz the only character who has physically appeared in every episode of the series so far.
- King only appears in Gus's crystal ball message recorder when Willlow was leaving a message for Gus.
- Eda only appears in an image of a news article titled "Mystery vendor floods market with dangerous human goods" when Luz is searching up information about the first human in the Bonesborough Library.
- This is also the first episode of the second season where neither Lilith nor Hooty appear.
- Luz speaks Spanish for the sixth time:
- "No te preocupes. Todo va a salir bien." means "Do not worry. Everything will be fine."
- "Nada funcionara a menos que lo haga funcionar." means "Nothing will work unless you make it work."
- Several search results appear when Luz is researching Philip. These include:
- "How to cure parasitic-"
- "Hexes for exes"
- "Hexside or St. Epiderm?"
- "How to survive a giraffe"
- "Hungry what eat?"
- "Hunting Basilisks"
- "Human wasps"
- The names on the statues refer to members of the crew, color designer Mari Alizor, and prop designers Aleth Romanillos and Khari Cephas.
- During the final scene, the sunset is the colors of the bisexual pride flag. Also, Amity's staff card has a shooting star on the back that has the colors of the lesbian pride flag.
- The colors of the pride flag are seen in Gus' crystal ball as its loads his message.
- One of the trials Luz had to face was taming a paper dragon. This is a reference to a creature Molly Ostertag created for one of her Dungeons & Dragons campaigns.
- The statues in the Looking Glass Ruins initially had their own individual designs, but were ultimately unified to make it easier to track them from shot to shot. 
Revelations and significant events
- Luz has been borrowing Gus’ library card frequently so she can visit Amity.
- Emira also implies that Luz has been walking Amity home from the library.
- Gus is revealed to have moved up two grades at Hexside in this episode.
- Mattholomule reveals that he has an older brother.
- Braxas is revealed to be Warden Wrath's son.
- Mattholomule had gone to Glandus before transferring to Hexside.
- Several revelations can be seen in Luz's search results.
- The name of the human who once lived on the Boiling Isles is Philip Wittebane.
- The portal to the Human Realm is intrinsically linked to Philip.
- The Boiling Isles use a similar calendar system as the Human Realm, as Philip was recorded to have donated his book in their equivalent of the 1600s.
- Amity admits to her siblings that Luz's arrival changed her; thinking and feeling things that she never did.
- This culminates at the end of the episode, where Amity gives Luz a kiss on the cheek.
- It is explicitly revealed that Amity dyed her hair because her mother likes it green.
- This was previously stated by Dana Terrace in a Reddit AMA.
- At the end of the episode, she dyes it a shade of purple. She also has her bangs cut shorter and no longer ties them back.
- Luz mentions what Gwendolyn revealed to her in "Keeping Up A-fear-ances" - that she is not the first human to visit the Boiling Isles, and that the previous one left a diary in the Bonesborough Library.
- Amity no longer wears her necklace, having broken it in "Escaping Expulsion".
- Gus has a "Bad Girl Coven" t-shirt, which was shown in "Something Ventured, Someone Framed".
- Mattholomule also mentions the events of this episode.
- The poster in Amity's room is the left half of the Azura illustration from "Covention".
- Nik Dodani makes his voice acting debut with Gavin.
- Through the Looking-Glass - The title is a reference to the novel written by Lewis Carroll, sequel to Alice's Adventures in Wonderland.
- Clash of the Titans - One of the movies seen in the newspaper clipping, War of the Titans, may be a reference to the 1981 fantasy film based on Ancient Greece.
- Planet of the Apes - One of the movies, Planet of the Humans, is based on the title of this classic sci-fi film.
- The Lesser Key of Solomon - The head librarian Malphas is based on the Goetic demon of the same name.
- Relativity - The physics-defying infrastructure of the Forbidden Stacks mirrors the optical illusion portrait made by M. C. Escher.
- Edwardian era - The archives of the "Deadwarian era" is a pun on the term for the era of Great Britain from 1901 to 1910.
- Gravity Falls - One of the books in the Forbidden Stacks resembles the journals from Gravity Falls.
- The Simpsons - The Keeper saying "I'll call the hounds" is a reference to Mr. Burns saying "Release the hounds".
- The Adventures of Prince Achmed - Philip Wittebane's backstory while in the Boiling Isles is done in silhouette animation, which is a reference to the 1926 animated film.
- Pokémon - The face of the illusion monster used to scare off intruders in the graveyard resembles the Pokémon Shellder.
- Eden Riegel is credited as voicing Boscha in the credits, despite Boscha not appearing or speaking in the episode.
- In the Canada broadcast, the episode is erroneously listed as the second season's seventh episode.
- Emira's beauty mark is missing at the beginning of the Blight Manor scene.
- Additionally, Edric's reflection briefly appears with a longer face.
- When Amity rushes back inside after kissing Luz she pushes the door open, however in the next shot it closes like it was pulled open.