When his father disappears, Jake Wilde is desperate to find him. Jake believes he knows exactly who to blame for the disappearance: his mysterious godfather, Oberon Venn. After getting himself kicked out of boarding school, Jake comes to Wintercombe Abbey, Venn's estate, where he tries to unravel his father's disappearance.
Jake learns that his father and Venn, along with Venn's servant Piers, had been experimenting on a obsidian mirror called the Chronoptika. The Chronoptika allows a person to travel through time, and Venn wanted to use it to bring his wife Leah back from the dead. While experimenting with it one day, David, Jake's father, vanished through the mirror, and no one has been able to find him since. Meanwhile, Sarah, a girl who time-traveled back from a Bad Future, Maskelyne, a sorcerer who claims to be the original owner of the mirror, and his questionably-girlfriend Rebecca are all trying to obtain the mirror for different reasons. The leader of the world in the Bad Future also time travels back to try and stop Sarah.
Besides the Chronoptika and everyone after it, Wintercombe Abbey is bordered by a forest said to belong to the Shee, and the Queen of the Shee, Summer, wants Venn to return to them. Gideon, a human boy taken by the Shee, wants Jake to help him get free and back to the time he came from, since if he leave the wood he will die, being as he is a human who is hundreds of years old.
Obsidian Mirror was followed by The Slanted World and The Door in the Moon.
Obsidian Mirror contains examples of
- Affectionate Nickname: Maskelyne always calls Rebecca "Becky".
- And I Must Scream: Going into the mirror without a bracelet or protection apparently forces one to live The Slow Path in some kind of spacetime void until it decides to spit one back out again. Maskelyne did it deliberately, being about to be police-raided.
- Bad Future: Sarah is from one; she traveled through time to try and prevent it from happening.
- Baleful Polymorph: A typical Shee punishment.
- Big Bad: Janus is implied by Sarah to be one. He rules the world in the future she's from.
- Cargo Envy: Are you really jealous of a mirror, [Rebecca]?
- Despair Event Horizon: For Venn, it was the death of his wife. For Jake, it's his father's disappearance.
- Disappeared Dad: David to Jake. This trope is what kicks off the story, as Jake is desperate to find his father again.
- Driven to Suicide: Discussed trope. When relating the history of the Chronoptika and how he came to have it, Venn admits that at the time David and Piers were working on it they were also caring for him, because after Leah died he became suicidal.
- Interrupted Suicide: After their first failure Sarah has to talk him out of shooting himself on the assumption the mirror will never work.
- Entitled to Have You: How Summer views Venn. She was the Romantic Runner-Up the first time around when she lost to Leah.
- The Fair Folk: The Shee, and how.
- Our Genies Are Different: Piers is heavily implied to be a genie, what with his ability to acquire clothing and various tools out of nowhere, his uncanny cooking and electrical skill, and the fact that Maskelyne is able to trap him in a china pot.
- God Save Us from the Queen!: Summer, Queen of the Shee.
- Half-Human Hybrid: The Venn family is rumored to be half-Shee.
- Icy Blue Eyes: Venn has these, befitting his status as an Ice King and as the implied Winter King of the Shee.
- I Lied: Gideon is on the receiving end of this twice, once from Jake and once from Sarah.
- Ice King: Venn is one, cold and distant, and implies he has been like this his whole life except when he was married to Leah. Played with in that it's implied that he is the Winter King of the Shee, and the counterpart to Summer.
- Identical Grandson: Sarah is easy to mistake for her grandmother Leah. Her and Venn's first interaction is a Wrong Name Outburst on this.
- I Just Want to Be Normal: Gideon just wants to go back to the time he came from and live as a human again.
- Kid from the Future: Sarah who is actually Venn's great-grandaughter.
- Last-Name Basis: Venn's first name is Oberon. Most people just call him Venn.
- The Lost Lenore: Leah to Venn. his desire to get her back kicks off the experiments with the mirror.
- Luke, You Are My Father: A variation. Before she leaves, Sarah tells Venn that she is his great-grandaughter.
- The Needs of the Many: Sarah wants to destroy the mirror to save the future. If she can destroy it the world will be saved, but there will be no way for Venn and Jake to get Leah and David back. Sarah tries to get them to see that the fate of the world is more important, but they don't see it like that. See also What Is One Man's Life in Comparison? below.
- Our Time Machine Is Different: It's an Obsidian Mirror.
- Parental Abandonment: Jake suffers from this trope, though in his father's case it was unintentional. His mother is said to be alive, but she doesn't seem to have much time for or interest in her son, and is only mentioned in passing in the first book. Sarah also suffers from this, though her parents are explicitly stated to have been arrested by the Big Bad of the Bad Future.
- Portal to the Past: How the Mirror works.
- The Reveal: Two-fold. The first is that Sarah is Venn's great-grandaughter. The second is that her existence proves that Venn will succeed in bringing Leah back, because he and Leah had no children before she died. To prove that her great-grandmother is Leah and not Summer, Sarah gives Venn a diamond brooch that he buried with Leah.
- The Rival: Summer views Leah as a romantic one, and she calls Leah one to Venn's face when he begs her to let him go through the Summerland to bring Leah back.
- Sense Freak: Gideon gets a brief moment at the end of The Slanted Worlds, being shocked that Piers' soup tastes "of...things" in comparison to Shee food.
- Trapped in the Past: Sarah wants to break the mirror to keep Janus from using it to conquer the world. If she succeeds, she'll suffer from this trope, but she is willing to do it. David also suffers from this trope in The Slanted Worlds.
- Time-Travel Tense Trouble: Combined with Write Back to the Future. Jake gets a letter from his father that is written using a variety of tenses because David has no idea when Jake will see the letter.
- Unfazed Everyman: Wharton's job is to deliver Jake safely to Wintercombe Abbey, but he ends up sticking around for the whole story. All things considered, he handles the discovery of the experiments on the Chronoptika, Venn's scheme to bring his wife back, that Piers is more than human, that Sarah is from a Bad Future, and that David is lost time pretty well. He even steps up to the plate when Venn and Jake vanish through the mirror and Piers goes missing to keep the mirror safe himself.
- What Is One Man's Life in Comparison?: Overlaps with The Needs of the Many. Sarah asks Venn and Jake a variant of this question after she tells them that in the Bad Future the Chronoptika is destroying the world. Neither of them really care, seeing as both of them want their loved ones back and need the mirror to achieve their goals.
- You Already Changed the Past: At the end of The Obsidian Mirror, Sarah tells Venn that he does successfully rescue Leah, and she knows this because she is their great-granddaughter. Only problem is, he hasn't already done it yet so now he has to figure out how.
- You Killed My Father: Jake accuses Venn of this, and the latter actually seems shocked that anyone could believe he would hurt David, who was his best friend. Jake later admits that he needed someone to blame for his father's disappearance, and Venn was the easiest choice.