Oroborus was the eleventh episode of K9. It was written by Deborah Parsons, directed by Daniel Nettheim and featured John Leeson as K9 Mark 2, Keegan Joyce as Starkey, Philippa Coulthard as Jorjie Turner, Daniel Webber as Darius Pike and Robert Moloney as Alistair Gryffen.
K9 notices a change in behaviour in his friends and discovers time itself is being disrupted. Small chunks of time are being eaten away. A Time Snake has invaded the mansion and Starkey makes a discovery about his own parents that means he alone can face the Oroborus. He offers himself as a meal to defeat the creature.
At the Gryffen house, the STM suddenly activates and starts pulling everything in the room towards the vortex. Gryffen and Starkey express their disbelief the STM could have turned on by itself. K9 registers the power source as unknown. He fires on the STM, locking off the plasma thrusters and shutting it down. After K9's long and detailed explanation of how he did it, Darius and Jorjie walk in, wondering what happened. Gryffen suspects someone has touched the STM, but Darius and Jorjie say they haven't, as does Starkey, who has a strange itch on his arm. Gryffen determines someone or something has breached the vortex. He sends K9 to search the house.
Darius gets his payment from Starkey for a pair of resistors which don't work. Starkey witnesses a weird distortion and loop, when Jorjie complains about Darius. K9 returns to Gryffen and tells him he has found no presence. That night, K9 wakes next to Starkey and tries to warn him of something, but time suddenly reverses and K9 goes back to sleep. Starkey feels the same strange itch as before. That morning, Gryffen is cooking breakfast when Starkey walks in. Gryffen is startled and drops an egg. Time loops and his dropping the egg repeats. Starkey keeps feeling the same strange itch and starts sneezing. Gryffen wonders if he's allergic to something. Gryffen decides to check and takes a blood sample from Starkey.
Gryffen finds a strange mark on Starkey's arm. Starkey tells him it has suddenly become itchy, which it never had before. Darius returns back from shopping, confusing Gryffen as he thought Darius went shopping the day before. Darius tells Starkey to pay for the resistors and Starkey tells him he paid him yesterday. Darius refuses to believe it and demands he pay up, starting an argument. Starkey calls Jorjie, thinking she'll back him up, but she says Darius gave him the resistors yesterday and he didn't pay him. Even though K9 didn't witness it, he scans Starkey and determines he isn't lying.
Starkey gives up and pays Darius. As K9 records it, a "temporal error" occurs, reversing time. Starkey talks to K9 in his bedroom. He wonders if Jorjie lied or if he really didn't give Darius the money. K9 detects a temporal loss; he lost seven seconds. Starkey researches schizophrenia and tells K9 he heard voices and saw faces as a child. He hopes they are memories. K9 tells Starkey to relax when he thinks he's going mad. K9 has had similar moments.
Darius asks Gryffen if he's found out what happened to the STM, wondering if it has been sabotaged. Both Gryffen and Darius say it wasn't them. Gryffen asks Darius who else was here. His question is answered when Starkey walks in. Gryffen tells Starkey his blood results are ready and goes to have a look. Gryffen is shocked at the readings. Starkey's body is producing strange antibodies. K9 scans them and confirms they are alien. Darius assumes he's an alien but Gryffen says Starkey's immune system is capable of defending against alien pathogens. Darius insists Starkey's an alien but K9 confirms he's human.
Gryffen states that alien immunology is beyond known science and only two people have experimented with it, a couple who tested the antibodies on themselves and their son. This leads Starkey and Gryffen to believe that the child is Starkey. In his bedroom, Starkey researches and analyses his alien antibodies, experiencing the itch again. A strange creature slithers through the cellar and the STM activates. Starkey asks K9's help but he is asleep. Starkey tries to stop the STM, using the same method K9 did. He succeeds, but Gryffen walks in, demanding to know what Starkey is doing. He finds someone has tried to access time, but when Starkey says it is the same as the incident yesterday, Gryffen and K9 tell him it never happened. Gryffen thinks Starkey switched it on.
Starkey leaves to get his stuff and K9 offers to join him. They notice that everyone has lost memories. K9 checks his memory of searching the house after the first breach and learns temporal loss corrupted the file of the cellar. They go down and discover strange tracks. Gryffen and Darius discuss Starkey tampering with the STM. Gryffen believe that Starkey is trying to find his parents. As Starkey and K9 search, they hear slithering. A time distortion occurs and K9 shuts down.
Jorjie goes to Gryffen and Darius, looking for Starkey. They tell her what Starkey was doing with the STM, but Jorjie wonders if the STM is what's causing time-shifts across London. When Gryffen says the STM is localised, Jorjie determines Starkey isn't tampering and turns on the news. The newsreader apologises that the King's birthday message was both not shown and shown twice. He interviews Brook Thomas, a spokesperson for a train company, about the news that all the trains are arriving on time. She says that the trains are 100% on time even if they are several hours late and that some trains are arriving even before they leave. The newsreader introduces the interview again and the spokesperson repeats her statement.
Back in the cellar, K9 reactivates and determines he has lost three seconds. Starkey finds some reptilian skin. Starkey shows Gryffen, who apologises for doubting him. The team realise the snake skin was shed. The snake is growing and is getting hungrier. Gryffen's analysis identifies it as an Oroborus, a time-consuming snake. Starkey decides to go alone to the cellar and stop it since he has alien antibodies. They plan to lure the Oroborus beneath the STM, then Gryffen will activate it. If the vaccine isn't effective, Starkey will be consumed.
Starkey goes to the cellar and faces the Oroborus, then slowly backs away. The Oroborous gets right beneath the STM room, but Starkey is trapped in a dead end and the Oroborus blocks the door. Gryffen activates the STM and sends the Oroborus away, while K9 finds Starkey. They return to the others, who are relieved to have them back. Later that night, when Starkey is in bed, Gryffen visits and apologises for doubting him. He gives Starkey a picture he found of two scientists he believes are his parents and bids him good-night as Starkey looks at the photo.
- K9 Mark 2 - John Leeson
- Starkey - Keegan Joyce
- Jorjie Turner - Philippa Coulthard
- Darius Pike - Daniel Webber
- Professor Alistair Gryffen - Robert Moloney
- June Turner - Robyn Moore
- Interviewer - Mark Hodson
- Brook Thomas - Michelle Atkinson
- CCPC - Josh Norbido
- CCPC - Jason McNamara
- CCPC - Maual Savdie
- CCPC - Dane Paltman
- Writer - Deborah Parsons
- Director - Daniel Nettheim
- Producers - Penny Wall, Richard Stewart, Simon Barnes
- Executive producers - Jim Howell, Grant Bradley, Steve Robbins
- Associate producers - Bob Baker, Paul Tams
- Supervising producer - Dale Bradley
- Co-Executive producer - Mark Blythe
- With special thanks - Sam Tromans
- Line producer - Pam Collis
- VFX Director - David Napier
- Series Production Designer - Jon Dowding
- Episodic Designer - Adam Head
- New K9 Design by - Paul Tams, Alex Kubalsky
- Series Director of Photography - Ben Nott
- Episodic Director of Photography - Tony O'Loughlan
- Music by - Christopher Elves
- K9 theme music by - Michael Lira
- Editor - Patrick Stewart
- Casting - Faith Martin and associates
- Episodic casting - Lisa Maloney
- Drama/Dialogue coach - Peter Kent
- Story Producer - Greg Walters
- Script Adaption - Michaeley O'Brien
- Production Accountant - Pru Donovan
- 1st Assistant Director - Peter McLennan
- Script Supervisor - Sue Ketchington
- Costume Designer - Joanne Thompson
- Makeup Designer - Sharon Robbins
- Puppeteer - David Pawsey
- Location Manager - Charles Boyle
- Sound Recordist - Ian Grant
- B Camera Operator - Dan Maxwell
- Gaffer - Steve Monk
- Key Grip - Billy Harmer
- Special thanks to - Space Furniture, Shredox, J. Barbour & Sons Ltd, Heath Williams at Firefly Lighting, Videopro
- Safety Supervisor/Stunt Coordinator - Danny Baldwin
- Transport Manager - Alister Ward
- Unit Manager - Graeme Suhr
- Post Production Facility - Cutting Edge Australia
- Head of Post Production - John Lee
- Sound Design - Warren Pearson
- In the Channel 8 newscast, the newsreader apologises to viewers who missed the King's birthday message and to those who watched it twice.
- The guest on the newscast is Brook Thomas, spokesperson for TubeCorp, which appears to have taken over responsibility for the London Underground.
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- The Oroborus is said to feed off potential energy, the same energy source used by the Weeping Angels. (TV: Blink)
Home video releases
This episode is featured in the following DVD sets:
- Series One complete box set, released in Australia on 29 September 2010. 
- A "vanilla" DVD called Alien Avatar, containing The Fall of the House of Gryffen, Jaws of Orthrus, Dream-Eaters, Curse of Anubis, Oroborus and Alien Avatar, released in Australia on 1 December 2010. 
- K9: Series 1: Volume 1, containing episodes 1–12, released in the UK on 31 January 2011 and in the US on 30 March 2011. , 
- K9: Ultimate Collectors Edition, containing the full first series, scheduled for release in the UK on 11 June 2011.