After getting up early, Lyra Silvertongue decides to travel to Will's Oxford and so leaves William Parry a note. Meanwhile Stanislaus Grumman uses a ring to summon Lee Scoresby to him; Lee finds himself heading towards the Yenisei to look for Grumman.
When Will wakes up after dreaming about a knife and the Torre degli Angeli as well as his father's letters to his mother, he goes downstairs to talk to Lyra about using her alethiometer to find his father. However, he can't find her and misses the note she left him so he wanders through the town.
Mary Malone, the scholar whom Lyra had met previously, tests the I Ching on the Cave. She is then visisted by DI Walters who asks her about Lyra's visit the day before. After Lyra enters, Mary pushes her into a lift to warn her about the policeman in her office. However, Walters discovers them and asks them into the office to talk to them.
He asks Lyra about why she is in Oxford, why she isn't in school, and about Mary Malone and her work before surprising her in asking whether Will is with her. Lyra lets slip that he is and regrets it but Mary asks to speak to the officer before gesturing to Lyra to run. Lyra flees and gets picked up by Charles Latrom in his car who takes her to Summertown. When he drops lets her go, she hurries off but he reminds her about her bag. After Latrom drives away, she realises that the alethiometer has gone and that Latrom has stolen it.
In the North, Lee Scoresby visits the Samirsky Hotel to ask questions about Grumman. An old man tells him about the life of Grumman and how he became a shaman and then tells him that he heard that Grumman was dead. However, Sam Cansino (who works in the hotel) tells Lee that she heard that he survived the trap which he was thought to have died from and that Lee should visit the Observatory where he worked.
Mary continues to work with the Cave, trying to get it to speak with words (which Lyra had recommended before) but receives no answers. In Cittàgazze, Will discovers Angelica staring at the tower and sees someone in the tower. Will asks her about the tower and the Guild. After still not getting any answers, Mary leaves her office and is told by a man that the girl, Lyra, got away.
At the Observatory, Lee asks Dr Haley there about Grumman who he says is a heretic. Lee leaves but is shot at; he shoots back and kills Haley but guards from the Magisterium come out and surround and imprison him. Mary is visited by her sister and her children and they talk about Mary's work and a possible breakthrough.
Meanwhile at the café, Will discovers the note Lyra left and goes through the window to find her sitting on a bench, upset. He begins to scold her but then sees how sad she is. Lyra tells him that the alethiometer was stolen but then remembers that Latrom gave her a card giving her his address.
Kaisa visits Iorek Byrnison to tell him about the Magisterium's attack on the witches. Kaisa notes that the bears are leaving the North as the food is disappearing. Kaisa says that the witches are looking for Lyra and Iorek tells her that she followed Lord Asriel through the window.
Marisa Coulter arrives at the Samirsky Hotel to speak to Lee who is chained. She tries to get him to tell her where Lyra is but he refuses and convinces her that she'll never be able to extract that secret from him as he loves Lyra too much. Defeated and angry, she leaves.
Will and Lyra enter a cinema where they watch Paddington. Lyra discovers popcorn and Lyra tells Will that she lost her best friend and that she wants to talk to him and apologise. At the hotel, Marisa receives a message from Lord Boreal saying that he knows where Lyra is and she goes upstairs to release Lee after their conversation earlier and her realisation that he loves Lyra. She tells him that, should he find the girl, he should keep her safe which Lee promises to do. Lee decides to find a boat and get to Grumman.
On her bed, Mary experiments with the I Ching and the Cave, in her office, responds to this interaction and she reads a line from the I Ching book. At Limefield House, Boreal greets Will and Lyra (who give false names) and invites them in. Boreal shows them the stolen alethiometer and reveals that he knows both their real names. Lyra remembers seeing him at the party in London. After refusing to give it back, Boreal makes an offer: if they give him the knife in the Torre degli Angeli, then he will give them the alethiometer.
"Theft" comes from the title of the ninth chapter of The Subtle Knife.
- Main article: His Dark Materials (TV series)#Cast
- Dafne Keen as Lyra Silvertongue
- Ruth Wilson as Mrs Coulter
- Lin-Manuel Miranda as Lee Scoresby
- Amir Wilson as Will Parry
- Ariyon Bakare as Boreal
- Andrew Scott as John Parry
- Simone Kirby as Mary Malone
- Ruta Gedmintas as Serafina Pekkala
- Sasha Frost as Reina Miti
- Nina Sosanya as Elaine Parry
- Bella Ramsey as Angelica
- Lewis MacDougall as Tullio
- Angus Wright as Dr Haley
- Jamie Wilkes as Pale-Faced Man
- Henry Miller as a porter
- Kirsty Besterman as Sam Cansino
- Nigel Cooke as Seal Hunter
- Julie Hale as Zoe (Mary's sister)
- Frankie Hervey as Louise
- Alfie Todd as Ben
- Joe Tandberg as Iorek Byrnison
- Cristela Alonzo as the voice of Hester
- Kit Connor as the voice of Pantalaimon
- David Suchet as the voice of Kaisa