Lord of Light is set on a planet colonized by some of the remnants of "vanished Urath," or Earth. The crew and colonists from the spaceship Star of India found themselves on a strange planet surrounded by hostile indigenous races and had to carve a place for themselves or perish. To increase their chances of survival, the crew has used chemical treatments, biofeedback and electronics to mutate their minds and create enhanced self-images, or "Aspects," that "strengthened their bodies and intensified their wills and extended the power of their desires into Attributes, which fell with a force like magic upon those against whom they were turned." The crew has also developed a technology to transfer a person's atman , or soul, electronically to a new body. This reincarnation by mind transfer has created a race of potential immortals and allowed the former crew members to institute the Hindu caste system, with themselves at the top.
The novel covers great spans of time. Eventually, the crew used their now-great powers to subjugate or destroy the native non-human races (whom they characterize as demons) while setting themselves up as gods in the eyes of the many generations of colonist progeny. Taking on the powers and names of Hindu deities, these "gods" maintain respect and control of the masses by maintaining a stranglehold on the access to reincarnation and by suppressing any technological advancements beyond a medieval level. The gods fear that any enlightenment or advancement might lead to a technological renaissance that would eventually weaken their power.
The protagonist, Sam, who has developed the ability to manipulate electromagnetic forces, is a renegade crewman who has rejected godhood, taking for himself the role of Siddhartha Gautama/Buddha. Sam is the last "Accelerationist": He believes that technology should be available to the masses, and that reincarnation should not be controlled by the elite. Sam introduces Buddhism as a culture jamming tool and strives to cripple the power of the gods with this "new" religion. His carefully planned revolt against the gods takes place in stages: "An army, great in space, may offer opposition in a brief span of time. One man, brief in space, must spread his opposition across a period of many years if he is to have a chance of succeeding."
(for characters, see descriptions below)
In a monastery, the deathgod Yama– assisted by Tak, the ape (formerly Tak the Archivist for the gods) and Ratri, Goddess of Night – assembles a clandestine radio transceiver to extract Sam's atman , or soul, from the "Bridge of the Gods," the planet's thick ionosphere, and restore it to a body. Sam's bodiless essence was projected by the gods into the ionosphere after his capture in the battle of Keenset. This mode of execution was used because the last time the gods killed his body, Sam returned and stole a new one from one of the lesser gods. When Sam awakes, he claims to be horrified to be back in the flesh, having been aware of his ethereal condition the whole time, and having experienced it as a blissful Nirvana. He wants to return, to "hear the song the stars sing on the shores of the great sea." Eventually, after meditation on and immersion in earthly senses, he returns fully to the world. Shortly after, an encounter with the god Mara, who had come to investigate the disturbances caused by Yama's machinery, causes the conspirators to flee. As they proceed, Sam muses on his past ....
Prince Siddhartha, entering old age, comes down to the city of Mahartha to obtain a new body. He finds that there have been changes while he has lived on his estates. Before getting the body, he must submit to a mind-probe, operated by the Masters of Karma , which will be used to determine his fitness for reincarnation. Those judged unfit are given diseased bodies or even reincarnated as animals such as dogs. The dogs then act as spies for the Masters. Siddhartha contacts Jan Olvegg, former captain of the Star of India , reveals himself as Sam, and realizes from what he is told that he cannot remain passive, and must proceed against the Gods. He raids the House of Karma, steals bodies for himself, Olvegg, and others, and causes the former Chief Master of Karma to be reincarnated as a dog. He then disappears to execute the next stage of his plan.
The Buddha appears, preaching a philosophy of non-violence that undermines the doctrine of obedience to the gods and the struggle for a better rebirth. Instead, he emphasizes the pursuit of Nirvana and release from the illusion of the world. The goddess Kali, realizing that this is Sam's work, sends her personal executioner, Rild, to kill Sam, but Rild falls ill and is found and tended to by the Buddhist acolytes, as well as by Sam himself. Because he owes Sam his life, Rild renounces his mission after he recovers. He becomes one of Sam's disciples, eventually exceeding his teacher's wisdom. He takes the name Sugata, preaching in earnest what Sam had done only calculatingly as a way to overthrow the gods. Yama descends to kill Sam. Sugata/Rild faces Yama on a treetrunk bridge over a river, knowing he cannot defeat the God of Death, but fighting him anyway. Yama kills Rild and proceeds to find Sam. However, Sam tricks Yama and escapes, promising to return with "new weapons." Sam also warns Yama against the machinations of Yama's beloved Kali, and in so doing makes a personal enemy of Yama.
Sam enters Hellwell, a huge pit where he had bound the demons centuries earlier. He negotiates with their leader, Taraka, for allies in his struggle. He frees Taraka to see the world above, but Taraka betrays him by taking possession of Sam's body, promising to resume the bargain "later." While in control of Sam's body, Taraka deposes a local maharajah and takes over his palace and harem. As Sam recovers control of his body, he finds himself becoming more like Taraka, enjoying the pleasures of the flesh. In turn, Taraka takes on some aspects of Sam, and ceases to revel in his life of pleasure. Sam tells him he has suffered the Curse of the Buddha , which is revealed to be a conscience and guilt. Soon after, Agni, God of Fire, arrives to kill Sam, finding instead two spirits in one body. Agni destroys the palace, while Sam/Taraka flees to Hellwell. They decide to free as many demons as possible before the gods arrive. However, even the full might of all the demons of Hellwell cannot stand against the gods. A mere four of the gods, Yama, Kali, Shiva, and Agni, are able to hold off the demons and pursue Sam. Despite his own powers, Sam is captured and Taraka leaves him. Sam is told that he is to be taken to Heaven and made an example of, lest the other gods try to emulate his rebellion.
In the place called Heaven, Yama and Kali are to be married. Tak of the Bright Spear is the Archivist of Heaven, but is suspect because he was fathered in lifetimes past by Sam. However, Tak's main concern is seducing comely demi-goddesses such as Maya, the Mistress of Illusion. Sam is more or less free to wander Heaven, even trysting with Kali, who would like to have him back as her lover. He preaches to any who will listen, and the gods allow this, hoping to flush out sympathizers. However, Sam knows of some of his old gadgetry locked away in one of the museums in Heaven, and with the help of Helba, the Goddess of Thieves, he attempts an escape using a belt that amplifies his powers. This fails, and Kali, disgusted with herself and with him, persuades Brahma to order a human sacrifice, namely Helba and Sam himself, to celebrate her wedding. Sam is set free once more to flee for his life, hunted by the White Tigers of Kaniburrha, some of whom may be reincarnated gods, perhaps even Kali herself. Tak attempts to protect Sam by killing the tigers, but is struck down by Ganesha. For this, Tak is sent out of Heaven in the body of an ape. The wedding proceeds, with Sam apparently dead.
Brahma is dead. He has been murdered by persons or gods unknown. Vishnu, Shiva, and Ganesha gather to quickly arrange a replacement. They decide that the only viable candidate is Kali. However, for her to be reincarnated as Brahma (a man), her short marriage to Yama must end. Yama is appalled at how coldly she accepts this. Next, Shiva is found murdered. Yama throws himself into investigating the deaths. His friend, Kubera, approaches the demigod Murugan and accuses him of the murders, finally addressing him as Sam. It appears that Sam has become part-demon, and can survive without a body. He displaced Murugan's spirit as Murugan was about to occupy a new body for the wedding feast. Kubera uncovered the deception by examining the brainwave records from the transfer. Instead of turning Sam in, Kubera offers to help him escape. Sam refuses, determined to kill as many gods as he can. Since Kubera's friend, Yama, is the obvious next target, Kubera tricks Sam, who has forgotten what a great warrior the fat old man was, and in a bout of Irish Stand-Down (in which two men take turns hitting each other until one cannot continue), knocks him out and prepares to flee on the giant bird Garuda. They recruit Ratri to stop Yama from interfering, and take her along. They flee to the city of Keenset, which is undergoing a technological revival, and is marked for destruction by the gods. Eventually, Yama, feeling betrayed by Kali and the other gods, joins them. With Yama's weaponry, and various allies, including the zombie army of Nirriti the Black, they fight a titanic battle of gods, men, and monsters, killing thousands of men, demigods, and eventually some gods as well. They go down in defeat, but not before dealing a crushing blow to the hierarchy of heaven. Yama apparently commits suicide, but some suspect that he has invented a remote reincarnation device. Ratri is exiled from heaven and condemned to wander the world in a series of homely bodies. Kubera had hidden himself in a vault, held in suspended animation. Sam, having proved himself unkillable, is instead projected into the ring of ions around the planet, known as the Bridge of the Gods. However, the gods win only a pyrrhic victory. The most powerful deities, such as Yama, Brahma, Shiva, and Agni, are now dead or sworn enemies of Heaven. Others have gone into exile rather than fight against Sam. While Brahma/Kali is exultant, Ganesha realizes that the days of Heaven are numbered, and he must look out for himself.
In the final story, Sam has been returned from Nirvana. Sam, together with Yama, Ratri, and Kubera, plan their next move in their campaign against heaven. They are joined by the drunken god Krishna, who is a great fighter when sober, and who has wandered the world since he went into exile rather than fight at Keenset. Meanwhile, Nirriti, a Christian and the former chaplain of the original ship, has amassed great power in the southern continent. He is laying waste to cities in his attempts to stamp out the Hindu religion that he hates. He has acquired enough technology to challenge anything the gods can muster, even if they resort to "the tall man of smoke who wears a wide hat," apparently a reference to a nuclear device. He is also allied with the freed demons. At first he seems to be a natural ally for Sam and Yama, but they entrust the demon Taraka with conveying a message to him, and Taraka is determined to fight Yama, to prove that Taraka is the mightiest being on the planet. Thus Taraka falsely tells them that Nirriti has refused, and instead they ally with Brahma to defeat Nirriti, if Brahma will consent to their demands. This alliance defeats Nirriti in a final battle, despite Ganesha's attempt at betrayal, but at a huge cost. Brahma (the former Kali), fatally wounded, is conveyed from the battlefield by Yama. Later, Kubera finds Yama with his "daughter", whom he calls "Murga". She is retarded, and Yama admits that this was due to a botched mind-transfer. Kubera, always ready to help his friend, uses his powers to stimulate Murga's mind. Sam sees Tak restored to a young body, as is Ratri. Sam then leaves, no one is sure where to. Myths build up around his life and his departure.