Just before midnight on 27 September 1970, two weeks before the end of the world, a young woman named Christine Summerfield is found in an abandoned building site, babbling and screaming. She calms down by the time she gets to the local police station, and eventually they release her, as it isn't worth holding her and they've just arrested someone much more important. Two unidentified young women have recently been killed and mutilated in a manner reminiscent of the Manson killings, and the police have just arrested a tall blond man who was behaving suspiciously in the area of the building site, and carrying unidentified electronic components and a sharp knife. Christine returns to the shop of her friend and drug dealer Lady Diamond, where she is attacked by a man who looks like Manson. After biting her leg open, he departs from the shop, and Christine is left with the confused impression that he somehow changed shape and sprouted wings as he left. Bleeding profusely from her leg, Christine returns to the police station, only to find no sign of any other policemen; the creature has forced its way through to the cell area, leaving the desk sergeant in a state of shock. Christine passes down a hallway which seems longer than physically possible, and reaches the cell with the blond man, who has surrounded himself with electronic components and is chanting a poem loop to contain the creature -- now a fleshy lump with a glass-mirror face and a single, bat-like wing.

Christine faints from shock and blood loss, and awakens the next morning to find herself in the blond man's flat. Her leg has been patched up with with a lump of false tissue which is growing into place. As she explores, she hears the blond man on the phone, arranging to change the terms of a treaty so the people on the other end will have access to the technology which will permit them to develop time travel. The blond man, who seems nervous and hesitant around her for some reason, introduces himself as Chris Cwej and apologises for getting her involved; since she interrupted the ceremony to control the sphinx, however, she has become a part of it, and he had no choice but to bring her here with him.

Cwej is an agent of a race of time travellers, having worked for them since they rescued him from one of their own kind, an Evil Renegade who travels through Time interfering with other civilisations, kidnapping people and then depositing them randomly throughout the Universe whenever he tires of playing mind games with them. The creature from the cell is a sphinx, a creature which feeds on extradimensional forces and excretes raw space-time. In the 26th century, the galaxy -- and possibly all of time and space -- is under threat by the Gods, creatures whose origins are still unknown; they may even be part of the fundamental forces which hold the Universe together. Most of the Gods have only recently woken, but some have been active for some time already. The Evil Renegade once fought the sphinx's gods, the Kings of Space, and fled with a bottle of sphinx-shaped space containing an entire Universe. After Cwej left him, the bottle fell into the hands of the time travellers, and they intend to plant a team in the bottle to carry on their culture should the Gods attack their home world. Cwej was sent into the bottle first, to prepare the way and open up the bottle from the inside so the survival team could get in. But he hasn't opened it yet.

Cwej shows Christine the sphinx which he captured; it is a control antibody programmed to remove all alien material from the bottle environment, and Christine guesses that it went for her and then changed its mind when it scented Cwej on her from their brief encounter at the police station. When she asks about the two previous murders, Cwej realizes from the sphinx's reply that there is something else present in London, a third party whose presence may endanger the time travellers' agenda. He uses the sphinx to open up a path out of the bottle into the real Universe, and another agent, Khiste, arrives in response. The time travellers have given Khiste the ability to regenerate his body tissue after injury, and he has changed his appearance, becoming a more and more efficient warrior until his skin looks like a suit of leathery, impenetrable armour. He ignores Christine, and warns Cwej that they have a problem outside; the sphinxes have come to the fortress on Simia KK98 to take back the bottle.

Christine accompanies Cwej and Khiste out of the bottle to see the truth for herself, and finds herself in a fortress on a psychedelically coloured world where the soldier agents of the time travellers are preparing to fight an army of sphinxes. The sphinxes fight by reshaping the space through which the time travellers pass, and Khiste has sent for reinforcements, a fleet of warships which could destroy the entire world. In a desperate attempt to prevent a battle, Cwej goes to speak with the sphinxes and makes a dangerous deal. The Kings of Space aren't interested in the machinations of the other Gods from whom the time travellers wish to hide, and if the sphinxes agree to let the time travellers use the bottle as a survival zone, then the time travellers will negotiate for the exchange of time technology. The sphinxes find this bargain acceptable.

Christine returns to the bottle with Cwej, where he releases the control sphinx under the terms of the new treaty. Christine is numbed by her realization that her world isn't real, and Cwej convinces her to stay with him where it will be safe, and she realizes there's nothing left for her in her old life in any case. On the one occasion when she returns to Lady Diamond's shop she sees a blonde girl sitting in her accustomed place, acting exactly as she used to, and returns to Cwej without even saying hello to her old friends. Over the next several days, Cwej travels the galaxy outside the bottle, contacting various other powers and making deals with them to trade time technology in exchange for alliances; the other powers don't necessarily have to fight alongside the time travellers, as long as they agree not to fight against them.

Christine is now sleeping with Cwej, and she accompanies him to a couple of the treaty signings -- one on a world turned inside out with a sun in the centre, and one where a sphinx pulls apart the body of a soldier, occupies the space within his body and uses it to sign the treaty. Cwej assures Christine that the soldier was specially bred in a vat for this purpose, but this doesn't make her feel any better. At one point Christine makes love with Khiste just to see what it's like, and is amused when Khiste doesn't understand the lack of resolution between them later. She also learns that she shares a surname with a friend of Cwej's, Benny Summerfield, who went missing and was presumed killed after her home world, Dellah, was taken over by the Gods.

Eventually, the control sphinx determines the nature of the third party in the bottle. Control of the bottle's operating system involves the use of psionic rituals, and the more advanced rituals require human sacrifice; but when Cwej first entered the bottle, his employers didn't fully understand the rituals required, and used their own technology to penetrate the final barriers. In so doing, they opened a connection between the bottle and the Vortex, a null-dimension which exists outside space-time. Over millions of years, by accident or design, various people, places and things have become lost in the Vortex, an eternity of living death without form; and now these creatures have entered the operating system of the bottle, infecting the very structure of its universe. These ghosts are now trying to change the rules of the Universe to make new bodies for themselves, and according to the terms of the new treaty, if Cwej can't expel the alien matter from the bottle Universe, the sphinxes will destroy everything and start over again.

Cwej's employers place a monitoring station in orbit to keep an eye out for the ghosts, and soon the people of Earth start to spot anomalies; strange flying animals are seen and the inhabitants of a mental institution in India transform into sphinx-like creatures. A fossil of a half-man, half-sphinx creature appears in a quarry, and Cwej realizes that although it's millions of years old it has only been there for a few hours; since the ghosts are now part of the bottle's operating code, they can affect all of Time and Space within. Cwej and Christine visit Simia KK98 to discuss the problem with the time travellers' scientists, and while there, Christine sees more clones being bred in vats of intelligent liquid; per the treaty, these will be used to take the biodata of the time travellers to sphinx-space.

The ghosts create a body for their collective intelligence, which takes the form of a living hole, the shape of a sphinx, between the bottle Universe and the outside world. Cwej attempts to convince the Horror to leave the Earth alone, but the Horror is only interested in destruction and begins to claw apart London. Cwej is apparently lost in the carnage, but Khiste takes Christine back to the monitoring station. The Horror has already blocked access to the outside Universe and it now attacks the monitoring station as those aboard make a desperate attempt to regain control. Christine, in a state of shock but determined not to hide from the inevitable, confronts the Horror head-on and demands an explanation. She is allowed into the heart of the Horror, where all of the people lost to the Vortex over the centuries have been joined into a single group being, controlled by a vast computer which was expelled into the Vortex in the 25th century following a battle with Chris' "Evil Renegade".

The Horror explains that, in the Vortex, all is revealed to be less than meaningless; even meaninglessness is a concept with some meaning. Obsessed with its own anger and pain, and granted a perspective over everything in all of Time and Space, the Horror knows that there is no reason at all not to destroy everything it encounters. Christine, however, points out that if there's no reason for anything then there's no reason not to be happy. The Horror is now a part of her Universe, where things aren't neatly resolved; therefore, she suggests that it take on human form and live as a human for thirty years to find out how things work in her world, rather than just destroying everything. The Horror is intrigued by her suggestion but isn't convinced that it's worth it, and in sheer desperation Christine challenges it to a game of rock-paper-scissors. She wins, best out of three, and the Horror agrees to her terms. The Earth is thus saved.

Cwej turns out to have survived the attack, but over the next few weeks as he recovers from his injuries he becomes difficult and standoffish. Finally on the night of 11 October, he leaves the flat for a walk, telling her to stay where she is. Instead, she decides to return to her old home for the first time in two weeks, but once there she finds a photograph of herself and her friends -- with the blonde girl from Lady Diamond's shop in her place. Finally realizing the truth, she returns to Cwej's flat and breaks open the padlocked room she has never entered, where she finds a vat of intelligent liquid programmed with the memories she thought were her own. She goes to the building site where she was found babbling by the police two weeks ago, but is too late; Cwej has already killed the clone which he has been growing in the tank for the past two weeks.

The advanced control procedures for the bottle require human sacrifice, and since Cwej was unwilling to kill even the "unreal" bottle people, he grew his own sacrifices and named them after himself and his friend Benny. The Christine Summerfields were programmed with the memories of a girl he met when he first entered the bottle, in order to make them real enough to count as sacrifices. The third Christine somehow managed to get away from him, and by the time he found her again her memories had settled into place and she had become too "real" for him to kill. The incidents with the sphinxes and the Horror have delayed him, but his orders still stand -- and with this third sacrifice, he has completed the ritual which will allow his employers to enter the bottle. And they aren't sending in a survival team; they're moving their entire culture into the bottle, uprooting themselves from their homeworld and invading the bottled Earth to make a new home as far away from the Gods as possible. This, of course, means the end of the world.

Christine never resolves her issues with Cwej, a generally good and decent man who deliberately sacrificed three people and brought the world to an end. The time travellers begin to reshape the Earth to their own needs, ignoring the human race as an irrelevance except for those who choose to surrender to a new life as the time travellers' servants. Christine leaves the bottle for the "real" Universe, where she sets off on a quest to find the time travellers' homeworld, which has now been abandoned and ruined so the Gods will never suspect the time travellers' race ever existed. As the last survivor of the bottle-world Earth, Christine decides to find Benny Summerfield, the closest thing she has to family in this Universe. If she can't do that, she will find the Gods, whom she suspects are inhabitants of the Universe beyond this one. Perhaps if she continues moving onwards and upwards, through different levels of reality, she will some day find the one which is really real.