Spring was the first story in the audio anthology, Circular Time, which comprised the ninety-first release in Big Finish's monthly range. It was written by Mike Maddox and featured Peter Davison as the Fifth Doctor and Sarah Sutton as Nyssa.
It featured the Doctor meeting another Time Lord who had "gone native" on an unnamed world inhabited by an avian species. It was perhaps most notable for its theme of how to construct a valid system of jurisprudence.
The Doctor and Nyssa land on a planet on instructions from the Time Lords. The Doctor has been tasked with a mission to convince fellow Time lord, the cardinal Zero, to return home and take his place on the high council. The native species on the planet appear to be an avian species. The Doctor and Nyssa stumble onto an ongoing trial for Redklaw who stole food but a child of the species is publicly injured as well because the law dictates that the guilty party as well as one of their closest of kin whom they care about most must be punished and Nyssa impulsively interferes, ignoring the Doctor's warning. While trying to calm the situation, the Doctor discovers that they have been expecting him.
When they are brought to the city in the trees by Carrion, she explains that Zero had concluded that the Time Lords would send the Doctor to persuade him to return. They are brought before Zero and throughout the course of the conversation many surprising facts are revealed to Nyssa about the Doctor. More importantly, the Doctor explains that the Time Lords have sent him because the native avian species on the planet have been developing at an alarmingly unnatural rate and they "trust" the Doctor's judgement to survey and potentially deal with the situation. Zero assures the Doctor that he has not interfered in any direct way in their evolution and attempts to persuade him that he simply lives among them, despite the fact that they refer to him as their "prophet" and that he is trying to help them "return to the sky". He then takes them to the hatchery and explains the intricate symbiotic hatching process of the avian species, including a plant called the Yolk of Darts, a yellow flower that is dangerous and poisonous enough to cause a Time Lord to regenerate and acts as a defense mechanism for the hatchery. He then points out the great city of "Platch" to them, explaining that they will be going there tomorrow because Zero is to act as a judge, jury and executioner because a murder has occurred there for the first time in six years. The Doctor is disgusted with this but there is nothing much he can do for now and so begrudgingly agrees to accompany Zero tomorrow and retires to his sleeping quarters, a nest, for the night.
That night, the Doctor is quietly visited in his temporary nest quarters by Snowfire, who explains that her father Willowsap, is the avian being judged tomorrow because he had a dispute and killed a neighbour, being prone to moods since her mother died. However, since she is his closest living kin most precious to him, she will almost surely be killed as well since the whole neighbourhood saw her father commit murder and he will most surely be judged guilty. She further explains that the entire population reject the current system of justice, believing that the innocent should not have to suffer the crimes of the guilty, however, they cannot operate outside the law and the Doctor now realises what Zero meant by "not interfering", in that he won't interfere preferring to keep things the way they are currently. He promises to help her and tells her to leave for now.
Nyssa, awoken by the stir, finds the Doctor who tells her they need to enact a plan quickly and he has something in mind. He then instructs her to go back to the TARDIS. The Doctor then visits Zero in his room and wakes him up, only to find Zero "acting", exclaiming that the Yolk of Darts has been brought to his room and "accuses" the Doctor of having brought it (while the gloves from earlier lie in the corner, Zero brought it himself) and the Doctor realises that he has been set-up by Zero. Zero, while shouting, touches the fruit and "dies", falling into the river where his TARDIS is located, buried at the bottom. He then re-emerges, having regenerated into one of the avian species and the Doctor notes that the plant must've altered his Gallifreyan DNA to be partially avian. Carrion arrives to inquire what happened and Zero explains that he killed their "prophet" (ie himself), and that in order to be punished, according to the law, the Doctor, his closest living "relative" (since they are the same species) must be killed as well. The Doctor, picking up on the hint, flees with Nyssa and they get back to the TARDIS in time to take off. Zero explains that with no way to punish the Doctor, and since he will never return, he cannot be punished as well, meaning that this calls for a revision of the entire justice system. He explains that there must be an immediate pardon for all awaiting trial, thus sparing Snowfire and himself, and that they will begin to base justice only on punishing the guilty party, while meanwhile it is revealed that the Doctor, having realised Zero's plan, went along with it as well, as Nyssa later realised.
- The Doctor - Peter Davison
- Nyssa - Sarah Sutton
- Hoodeye - Jamie Sandford
- Redklaw - Toby Longworth
- Carrion - Lois Baxter
- Snowfire - Teresa Gallagher
- Zero - Hugh Fraser
- The Doctor mentions jelly babies and his fourth incarnation's scarf.
- Zero is from the Prydonian Chapter of Time Lords, the same chapter that the Doctor belongs to.
- The Council of the Great Mother is a Time Lord organisation.
- The Doctor has George Mallory's gloves after apparently accompanying him on his journey up Mount Everest.
- Zero describes the Time Lords as old men with high collars as opposed to their usual description as Gods.
- Gallifrey has temporal projectionists, Time Lords able to see into the near future based on current developments.
- Zero cannot learn the avian language or speak it because his throat is the wrong shape and he doesn't possess a syrinx, so he had his TARDIS buried under the lake because he still needs its translation circuit to communicate with them.
- Gallifreyan protocols dictate that Time Lords must regenerate before beginning exile.
- Zero describes the Yolk of Darts as like a bottle of decent red seña wine.
- Zero used to do acting in Athens.
- Nyssa refers to the Doctor failing to detect the Master's TARDIS.
- According to a 20 November 2006 blog post, Mike Maddox wrote this story based on a short story by Paul Cornell.
- This was the first in a series of stories named after seasons.
- Lord Cardinal Zero's regeneration at the end of this story is the only instance of a Time Lord regenerating into a different species.
- This story is set between Time-Flight and Arc of Infinity.
- Nyssa suggests the Doctor might be afraid of heights after his fourth incarnation's fatal fall from the Pharos Project's telescope on 1 March 1981. (TV: Logopolis)
- Zero is aware of the destruction of Traken. (TV: Logopolis)
- Zero refers to the Doctor's first trial on Gallifrey and his consequent forced regeneration into the Third Doctor. (TV: The War Games)
- Zero sarcastically asks the Doctor if the Time Lords have sent him to stop the creation of the avians' empire or lock them in a tunnel, setting them back over a thousand years. (TV: Genesis of the Daleks)
- The Doctor wakes Zero up by yelling, "Look out, vampires in the Capitol!" (TV: State of Decay)
- Zero snidely comments about the Doctor being President of the High Council. (TV: The Five Doctors)
- Nyssa comments that she doesn't understand how the Doctor knows there's another TARDIS around when he failed to recognise the Master's TARDIS last time they encountered another TARDIS. (TV: Time-Flight)