If PMar returns, they are welcome to any or all of this answer since they found the title.
The story opens with Paul Jonas, a British infantryman in an apparent part of the Western Front of World War I. Wounded, he has a vivid dream in which he meets a "bird-woman", and after he wakes up, he discovers one of her feathers with him in the trenches. Realizing that the world is not as it seems, he flees, pursued by his comrades Finch and Mullet, who suddenly have different appearances. Suffering from almost complete memory loss, he begins to travel through a series of bizarre worlds, seeking answers to who he is and his connection to the bird-woman. She appears to him in several guises as he travels, and is initially one of the few things he remembers from before the trenches.
Meanwhile, in the late 21st century, technology has advanced so that the internet has become a vast Virtual Reality network. The most realistic connections to the network are achieved by using an expensive, surgically implanted bio-port interface at the back of the user's neck called a 'neurocannula'. However, around the world, children are falling victim to a disease known as Tandagore Syndrome, which in its most serious form is a deep coma from which the patient cannot wake. Irene "Renie" Sulaweyo, an instructor in "virtual engineering" at a polytechnic institute in Durban, South Africa, is devastated when her younger brother, Stephen, falls victim to this disease. She and her former San technology student !Xabbu (pronounced with an unspecified clicking sound, as in the Xhosa language) begin to investigate what has happened and start discovering strange goings-on in the Net, including an evil hypnotic entity and the constant reappearance of a mysterious golden city. She seeks expert assistance from a previous instructor, Susan van Bleeck. But it soon becomes apparent that she has made powerful enemies: Renie is dismissed from her job, the apartment complex where she and her unemployed father Long Joseph live is burned down, and Professor van Bleeck is murdered. Renie turns to two of van Bleeck's acquaintances: a retired security expert and hacker called "Blue Dog Anchorite" and the French researcher Martine Desroubins. Blue Dog Anchorite informs the others that Otherland, the mysterious network where the golden city is located, was specially commissioned by a cryptic organization known as the "Grail Brotherhood", comprising some of the world's wealthiest and most powerful men and women, and that he is the only surviving member of the team who devised Otherland's security, his colleagues having died in unusual circumstances. With the help of Martine and Blue Dog, Renie, !Xabbu, Long Joseph and van Bleeck's assistant Jeremiah Dako break into Wasps' Nest, a mothballed military base in the Drakensberg which nevertheless contains equipment facilitating extended stays online. While Long Joseph and Jeremiah stay offline, she, !Xabbu and Martine (who remains in France) break into the Otherland network to reach the golden city.
In North America, Orlando Gardiner and his friend Sam Fredericks, famous contestants in the Middle Country, a Medieval fantasy gameworld, go on an apparently routine quest, where Orlando finds his own image of the golden city. While he is distracted by the image, his gaming character is killed, and he becomes obsessed with finding out what the city is and why it was shown to him. Following the trail of the city, he and Fredericks gain access to the online fringe community TreeHouse, from where they too find their way into Otherland.
Renie, !Xabbu, Martine, Orlando and Fredericks, along with several others, find themselves in an uncomfortable situation. In the simulation world, they are held prisoner by the king of Temilún (the golden city), who is none other than Bolivar Atasco, a former member of the Grail Brotherhood. Furthermore, they are unable to drop offline, and experience terrible pain if disconnected by others. Summoned to an audience with Atasco and his wife, they meet a mysterious man named Sellars, who claims to have gathered them. Sellars gives them a mission: they are to find Paul Jonas, who is at large somewhere within Otherland's many simulation worlds. But before the briefing can finish, the Atascos' home in the real world is assaulted by assassins working for the Grail Brotherhood. Bolivar and his wife are murdered, and Sellars vanishes. Even as the group flees Temilún, one of their "sims" – simulation bodies – is secretly taken over by John Dread, a murderous young man who directed the Grail Brotherhood's assault on the Atascos and who now seeks to learn about Otherland to his own advantage.
As they try to discover the motivations of the Grail Brotherhood — obviously not world domination, since they already control the world — they discover that they are unable to log off. They are trapped, and if they die in the network, they also die in real life. The series covers their adventures as they seek to uncover the truth and wake their loved ones from their comas.