Winter is closing in on the Doctor’s home, but at least he is no longer having the funny turns in which he claims that the Glass Men of Valcea are coming to avenge themselves upon him. While he tries to tend to his dying herb garden, his lodger Fitz reads the magical book Aja’ib and argues with fellow lodger Compassion, who wants to burn the books in the Doctor’s library to keep warm. Compassion, feeling irritated and constrained by the people around her, goes for a walk only to be attacked by a slavering beast; as winter closes in the town, they are venturing towards the warmth of the town centre, and the people therein. Meanwhile, the Doctor visits his friend Sally, who claims to be able to speak to her Jack Russell terrier Canine. She has given up on writing “realistic” novels, and has found that this has given her much greater freedom with her characters. As such, she has recently finished a fantastical novel in two parts; the first part set in a desert ruled by a scarlet Queen in a jam jar, and the second, a cold tale about a glass city ruled by the elephant king Daedalus, and surrounded by a network of space-time Corridors. The Doctor agrees to read it and offer his opinion, but he suddenly suffers another of his “funny turns”, and his left leg goes completely numb beneath the knee.
Despite radio warnings of severe snow conditions, three pensioners visit their local shopping centre for a day out, accompanied by Maddy Sharp’s adopted son Ian -- whom she found waiting for her in a cave while on her holidays, and who is the same age her own son Ian would have been if he had not died as a child. In the mall, they meet an eccentric young woman named Iris Wildthyme, who doesn’t tell the others that she has been waiting for Ian to arrive; she knows that his real name is Icarus, and that he is the key to what is about to happen. Winter is about to enter the shopping centre, and elsewhere, the Doctor is blundering into one of the most dangerous traps of his existence; Iris only hopes that she can get him to safety with a minimum of fuss. The power goes off in the shopping centre, and while the panicked patrons evacuate, Iris advises the pensioners not to follow. It’s not getting out that’s the problem -- it’s what’s about to come in. Giant owls smash through the skylight of the shopping centre and attack, and before Iris can stop them they have plucked up Nesta and flown off with her. Iris, Ian, Maddy and Big Sue must now get out to Iris’ bus, now their only protection from the creatures of winter.
The TARDIS takes the Doctor, Fitz and Compassion to the Federation starship Nepotist, which has been trapped in orbit around a vast city of glass. The Doctor insists upon helping, to the frustration of Captain Robert B. Blandish, who is used to being in charge of the situation; he allows the Doctor to accompany his away team, but orders Fitz and Compassion to remain aboard the Nepotist. Blandish, the Doctor, first mate Garrett, security guard Timon and communications officer Belinda beam themselves down to the glass city of Valcea, where the native Glass Men bring them before their leader Daedalus -- a giant jade elephant who appears fully aware that the appearance of Valcea in a space where it shouldn’t exist may threaten the delicate political stability of the Federation. When Daedalus refuses to explain his intentions, Garrett snaps and opens fire on him and the Glass Men for no apparent reason. Daedalus freezes the Federation men in force field prisons and orders the Doctor and Belinda back to their guest quarters. A friendly Glass Man named Marn, concerned about Daedalus’ unpredictable mood swings, allows the Doctor and Belinda to escape, and the Doctor slips back and frees the Federation men from the force fields. As the Federation men transport back to the Nepotist, however, the device which the Doctor was using to circumvent Daedalus’ jamming fields overloads, leaving the Doctor and Belinda trapped in Valcea.
Upon returning to her bus, Iris sends a call to the Doctor for assistance, and the TARDIS answers the call, transporting Fitz and Compassion to the snowy wastes outside the bus -- where, according to the TARDIS’ navigational system, they have materialized somewhere called the Enclave, in forty-three different places simultaneously. When they emerge from the TARDIS, they find that they can still see the Nepotist orbiting overhead; they have materialized outside Valcea, as have Iris’ bus and Maddy’s Morris Minor, and they are surrounded by a network of Corridors which stretch into forbidden areas of time and space. While Fitz and Compassion meet Iris and share their stories with her, Icarus, who appears to be in some pain, tells Maddy and Big Sue that he must be taken to his father -- and offers to restore their youth if they help him. Despite her shock and confusion over these weird events, Maddy agrees to help her adopted son, and she and Big Sue drive off into the Corridors in their Morris Minor, heading for Valcea. When Iris realizes what has happened, she follows them, but the bus is attacked by the giant owls, who fly off with Iris and Fitz and leave Compassion alone in the bus.
Daedalus summons the Doctor to answer for his actions, and Belinda and Marn, worried that Daedalus is about to plunge Valcea and the Federation into war, depart into the Corridors to seek allies amongst the Ghillighast, ancestral enemies of the Glass Men. Upon arriving, they are welcomed as honourable guests, for the Ghillighast have learned how to manipulate lice to discover the secrets of the Universe, and have been expecting the arrival of Belinda since the beginning of Time. As the honoured Bride of their lice god, Pesst, her arrival heralds the dawn of a new age of history in which all is now unforeseen. Belinda, who has always felt unappreciated in her job and has suffered since childhood from terrible dreams of being turned into a giant helpless squid, is delighted by her new position, and at Marn’s urging, the Ghillighast agree to return with them to Valcea and oust the corrupt Daedalus from power. Meanwhile, Daedalus reveals that he allowed the Doctor to free Blandish and the others as part of his master plan; he has always been jealous of the Doctor’s reputation as a troublemaker, and seeks his own brand of infamy. The necromancers of Hyspero were of no help, and they transformed him into a jade elephant when he sought to consult them; but in this form, he was able to find a new home in the Enclave and access to the Obverse beyond. With the alternate physics of the Obverse at his command, he has stretched Corridors throughout space and time, connecting planes and places which were never meant to meet, and spreading chaos and war throughout the Universe and all other Universes beyond.
Seeking warmth and companionship, the Doctor risks the harsh winter weather to visit the pub and the local Spiritualist Church; there, a medium in a trance tells him that though he may hate her for it at the time, Iris will act to save his life. The Doctor has been dreaming of twisted timelines and of camouflage flowers; is his whole past open to change now, or is he himself unreal -- a decoy created to prevent the real him from coming here? He has two hearts, his mother is a mermaid, and his left leg is swelling in a most peculiar manner as if something is growing within. Meanwhile, his friend Sally shares tea with her eccentric elderly next-door neighbour, Iris -- who tells Sally that she knows of the book she’s written, the characters she’s based on her friends, and the story which is closer to the truth than she can imagine. Perhaps by rashly setting down the true dreams of the Doctor and Iris, she has brought the danger of the Glass Men even closer -- but here in the Obverse, all can be made right again.
Garrett informs Blandish that he recognized Daedalus as a war criminal responsible for the destruction of Garrett’s home world, a peaceful planet dedicated to the study of mathematics and logic; before he could be brought to justice, Daedalus was spirited away by a shiftless time traveller named Iris Wildthyme. Daedalus allows the Doctor to watch as he deliberately provokes Blandish into opening fire on Valcea to diminish its capacity for war against the Federation, but prevents the Doctor from interfering. He claims to be acting as Time’s Champion, to forestall the evolution of the Glass Men into a threat greater than that of the Daleks, but the Doctor doesn’t believe him. As Valcea splinters about him and the Glass Men die in their hundreds, the Doctor has no choice but to flee to the safety of the Corridors; there, lost in their twisting, recursive lengths, he is reunited with Compassion. She tells him that Fitz and Iris are dead and urges him to return to the TARDIS and depart, but he refuses to do so, and decides to fit her receiver with a filter connected to the TARDIS to ensure that she no longer falls prey to random impulses from the local environment.
Maddy, Big Sue and Icarus are captured by Steigertrudes, warrior warthog women who roam the Obverse, destroying all artistic treasures they encounter. Their leader, Emba, recognizes Icarus for whom he is, particularly as his growing pains have ended and he has grown a pair of beautiful, angelic wings; intending to strike a deal with Daedalus, she agrees to help take Icarus the rest of the way to Valcea. Meanwhile, Fitz and Iris are dropped ib amongst other humanoids in the Owls’ larder, where a terrified Nesta accuses Iris of bringing the Owls and stirs up the angry primitives against them. Iris holds off the primitives with her hand blaster, and she and Fitz flee on a pair of horse-like animals presumably also kept here for food. As the Owls return, Iris and Fitz attempt to flee, but realize too late that they are being herded to the centre of the Owls’ habitat, where the eldest of the Owls is waiting for them. Using a cloak woven from the feathers of all the birds of the Enclave, it speaks to them, explaining that the Owls’ god, a great white bird, left its two hallowed eggs for the Owls to watch over, with strict instructions that they should not be allowed to hatch before their time lest catastrophe result. Daedalus stole one of the eggs and allowed the child Icarus to hatch prematurely, and the Owls must now travel to Valcea to confront Daedalus and destroy the child.
Blandish awakens from a fugue to discover that he has just destroyed Valcea utterly. Before he can react, the Nepotist is surrounded by the warlike Sahmbekarts, who accuse him of perpetrating an act of war and open fire. Despite all the precedent of his past heroism, this time Blandish finds he is unable to defend his ship adequately, and the Sahmbekarts capture the Nepotist and begin slaughtering its crew with delight; now they have a legitimate excuse to wage war on the Universe beyond the Enclave. Before they can use the Nepotist to take the war to the outside Universe, however, Blandish uses his command override to crash the ship on Valcea. He misses the city and crashes in the ice fields outside, but most of the invaders and crew are killed nevertheless; only Blandish and Timon survive, and they begin to make their way back to Valcea, where Blandish intends to exact revenge on Daedalus by triggering the last-resort suicide bomb implanted in his body. Meanwhile, Iris’ bus encounters a region of the Corridors where blue babies grow from the walls and floor, and when the Doctor attempts to investigate one of the babies reaches out and seizes his left leg, marking him. The Doctor refuses to let Compassion drive over the babies, and advises her not to dematerialize, as they are in an unstable time machine and an unstable region of space; before he can stop her, however, she does so.
Belinda, Marn and the Ghillighasts arrive in Valcea to find Daedalus apparently trapped and helpless, but as they prepare to celebrate their victory, Daedalus transforms Belinda into a giant squid, thus depriving the Ghillighast of their queen. At that moment Iris’ bus arrives, and as the Doctor attempts to take charge of the situation, Icarus arrives and is reunited with his father. As promised, Daedalus restores Maddy’s and Big Sue’s youth and returns them to Earth, but at that moment the Owls attack, bringing Iris and Fitz with them. The Doctor urges Iris and Fitz into the bus to safety, but is surprised when Iris immediately takes the bus out of time and space. She explains that she is in fact from the Obverse, and that Daedalus has extended the physical laws of the Obverse into the mateiral Universe, drawing other species into the war which will result from Blandish’s actions. The Doctor insists upon being returned to set matters right, but instead Iris takes him back to the shopping centre where she met the pensioners, where the TARDIS is waiting. She can’t let him go back, and the TARDIS knows why, which is why it has been taking him to the sites of so many dimensional rifts on Earth. One day, perhaps Iris will be able to explain; until then, all she can do is hope that he will understand one day why she acted as she did. Furious beyond measure but unable to change her mind, the Doctor storms off back to the TARDIS with Fitz and Compassion. Back in Daedalus’ throne room, the Owls set upon Icarus and tear him apart, but what happens after that -- the outcome of Blandish’s intended detonation, and the ensuing war and chaos as the fractured Corridors draw multiple Universes into the fray -- may never be known. Perhaps Iris removed the Doctor -- this incarnation of the Doctor -- so he would not know what happened next...
The man called the Doctor makes dinner for his lodgers and for his friends Sally and Iris. Fitz finds that Sally’s terrier Canine can speak to him, and it suggests that his attempts to make sense of the fictions he’s reading are doomed to failure. How can one thing be any more real than another? And if such a thing were possible, what would Fitz do if he found out that his own reality was the less real one? Here in the Obverse, perhaps all things are real at the same time, even if they contradict one another. The Doctor, meanwhile, admits to Sally that he’s read her book and found that it features elements of his own dreams, which he’s never told anyone; although Sally claims just to have made the story up, Iris claims that there’s no such thing. After dinner, the Doctor and Iris go walking naked in the snow, and Iris uses an icicle to slice open the Doctor’s swollen calf -- and a beautiful blue angel baby is born out of the Doctor’s leg, and flies off back home to the Obverse.