Arthur C. Clarke, 2001: A Space Odyssey (1968)

2001: A Space Odyssey (1968) is a science fiction novel by Arthur C. Clarke. It was developed concurrently with Stanley Kubrick's film version and published after the release of the film. The story is based in part on various short stories by Clarke, most notably "The Sentinel" (written in 1948 for a BBC competition but first published in 1951 under the title "Sentinel of Eternity"). For an elaboration of Clark and Kubrick's collaborative work on this project, see The Lost Worlds of 2001, Arthur C. Clarke, Signet., 1972.
The first part of the novel (in which aliens nudge the primitive human ancestors) is similar to the plot of an earlier Clarke story, "Encounter at Dawn".
Aliens keeping a watch on development of intelligent beings everywhere and helping where they can is an idea this novel shares with "Rescue Party", Clarke's first published story.
The opening of another Clarke story, "Transience", is set in the same period of human history as the first part of this novel; but the two stories are unrelated.

Plot summary

In the background to the story in the book, an ancient and unseen alien race uses a mechanism with the appearance of a large crystal Monolith to investigate worlds all across the galaxy and, if possible, to encourage the development of intelligent life. The book shows one such monolith appearing in ancient Africa, three million years B.C., where it inspires a starving group of the hominid ancestors of human beings to conceive of tools. The ape-men use their tools to kill animals and eat meat, ending their starvation. They then use the tools to kill a leopard that had been preying on them; the next day, the main ape character, Moon-Watcher, uses a club to kill the leader of a rival tribe. Moon-Watcher reflects that he is now master of the universe, but is unsure of what to do—but he'll think of something. The book suggests that the monolith was instrumental in awakening intelligence, and enabling the transition of the ape-men to a higher order, with the ability to fashion crude tools and thereby be able to hunt and forage for food in much more efficient fashion.
The book then leaps eons to the year 2001, detailing Dr. Heywood Floyd's travel to Clavius Base on the Moon. Upon his arrival, Floyd attends a meeting. A lead scientist explains that they have found a magnetic disturbance in Tycho, one of the Moon's craters, designated Tycho Magnetic Anomaly-One (TMA-1). An excavation of the area has revealed a large black slab; it is precisely fashioned to a ratio of exactly 1:4:9, or 1²:2²:3² (that is to say the thickness of the slab is exactly 1/4th the width and 1/9th the height). Such a construction rules out any naturally-occurring phenomena, and at three million years of age, it was not crafted by human hands. It is the first evidence for the existence of extraterrestrial intelligent life. Floyd and a team of scientists drive across the moon to actually view TMA-1. They arrive just as sunlight hits upon it for the first time in three million years. It then sends a piercing radio transmission to the far reaches of the solar system.
The book then leaps forward 18 months to the Discovery One mission to Saturn. David Bowman and Frank Poole are the only conscious human beings aboard Discovery One spaceship. Three of their colleagues are in a state of suspended animation, to be awakened when they near Saturn. The HAL 9000, an artificially intelligent computer, maintains the ship and is a vital part of life aboard.
While Poole is receiving a birthday message from his family back home, HAL tells him that the AE-35 unit of the ship is going to malfunction. Poole takes one of the extra-vehicular pods and swaps the AE-35 unit, which is critical for sustaining communication with Earth. Bowman conducts tests on the AE-35 unit that has been replaced and determines that there was never anything wrong with it. Later, HAL claims that the replacement AE-35 unit will fail. Apprehensive, Poole and Bowman radio back to Earth; they are told that something is wrong with HAL and are given orders to disconnect him. These instructions are interrupted as the signal is broken. HAL informs them that the AE-35 unit has malfunctioned.
Poole takes a pod outside the ship to bring in the failed AE-35 unit. As he is removing the unit, the pod, which he had left further from the ship, begins moving toward him. He is powerless to move out of the way in time and is killed by the impact; his spacesuit is ripped open. Bowman is shocked by Poole's death and is deeply distressed. He is unsure whether HAL, a computer, really could have killed Poole. He decides that he will need to wake up the other three astronauts. He has a long argument with HAL, with HAL refusing to obey his orders, insisting that Bowman is incapacitated. Bowman threatens to disconnect him if his orders are not obeyed, and HAL relents, giving him manual control to wake the sleeping scientists.
As Bowman begins to awaken his colleagues, he feels a cold chill; HAL has opened the inner and outer airlock doors to space, venting the ship’s atmosphere. The pressure on board is rapidly dropping as the ship is equalizing with the vacuum of space. Bowman makes his way into a sealed emergency shelter which has an isolated oxygen supply and spare spacesuit. He then puts on the spacesuit and re-enters the ship, knowing that HAL has killed the three hibernating astronauts. Bowman then laboriously disconnects the computer, puts the ship back in order and manually re-establishes contact with Earth. He then learns that the true purpose of the mission is to explore Japetus (the third-largest moon of Saturn), in the hope of contacting the society that buried the monolith on the Moon.
Bowman learns that HAL had begun to feel guilty and conflicted about keeping the purpose of the mission from him and Poole, which ran contrary to his stated mission of gathering information and reporting it fully. This conflict had started to manifest itself in little errors. Given time, HAL might have been able to resolve this crisis peacefully, but when he was threatened with disconnection, he defended himself, believing his very existence to be at stake.
Bowman spends months on the ship, alone, slowly approaching Japetus. A return to Earth is out of the question, as HAL's sudden decompression of Discovery severely damaged the ship's air filtration system, leaving Bowman with far less breathable air than either returning to Earth or waiting for a rescue ship would require. Hibernation is impossible without HAL to monitor it. During his long approach, he gradually notices a small black spot on the surface of Japetus. When he gets closer, he realizes that this is an immense black monolith, identical to TMA-1, only much larger, which the scientists back on Earth name "TMA-2", which is a misnomer because it gives off no magnetic force whatsoever.
He decides to go out in one of the extra-vehicular pods and investigate the monolith. Inert for aeons, the monolith reveals its true purpose as a stargate when it opens and pulls in Bowman's pod. Before he vanishes, Mission control hears him proclaim: "The thing's hollow — it goes on forever — and — oh my God! — It's full of stars!"
Bowman is transported via the monolith to a star system far outside our galaxy. During this journey, he goes through a large interstellar switching station, and sees other species' spaceships going on other routes, calling it in likeness to the 'Grand Central Station' of the universe. (This is rather different from the film, which portrayed the entire journey as surreal.)
He is brought to what appears to be a nice hotel suite, carefully constructed from monitored television transmissions, to make him feel at ease. Bowman goes to sleep. As he sleeps, his mind and memories are drained from his body. David Bowman is made into a new immortal entity that can live and travel in space; a Star Child. The Star Child then returns to our Solar System and to Earth. After slightly testing his newfound powers by setting off what can be assumed, several megatons of nuclear energy, Bowman reflects that he is now master of his universe, but is uncertain of what to do—but hopefully he'll think of something.