NOTE: The following version of this book was used to create this Study Guide: Haig, Matt. The Humans. Paperback edition. Published by Canongate, Great Britain, 2014.

The Humans is a tale of discovery, connection and the meaning of life, told from the perspective of an alien visitor to Earth who is waylaid on his mission by the various unexpected details involved in the typical human life.

The narrator described himself as being non-human and Andrew as being more alien than human from the little time the two spent interacting before Andrew was taken away. The narrator awakened in his human body, naked and on a motorway, confused by everything but observant of what was going on. He tried to make his way to Cambridge but was hit by a car, then when taken into an ambulance reacted with horror towards the humans and jumped out of the ambulance. He walked into a gas station where the clerk called the police on him, while he read a magazine in order to gauge the language. He ran away from the gas station and went to the campus of Cambridge University.

The narrator went into a bookstore and saw a book by Isobel Martin, Andrew’s wife, briefly reading it. He tried to reach Andrew’s office but was caught by the police and was taken to the station. The narrator had a voiceless "briefing" telling him that he must comply with everything now, that he had a mission to fulfill, and that being afraid among humans was understandable. The narrator was made to put on clothes, at which he mused upon the importance and value of clothes among the human race. He realized that he had been arrested simply for not wearing clothes which surprised him. The policemen started questioning him and called in a psychiatrist when the narrator gave strange answers. The psychiatrist questioned him and admitted him to a psychiatric institution. The narrator met his (Andrew’s) wife for the first time who was very concerned about him and then she went home after they spoke for a while.

The narrator then went to the dining area and met a patient named Zoe. Zoe asked the narrator some questions and they had a brief discussion about philosophy while the narrator took stock of the people around him. The narrator convinced a nurse that he only had temporary insanity and Isobel took him home. The "call from home" reminded the narrator not to become swayed from his mission or influenced by humans, who were a destructive race. The narrator absorbed as much information about the family as he could while resting in the bedroom. Isobel brought a TV into the room and turned on the news, which greatly confused the narrator due to its skewed priorities and bias. He started to plan his mission when Isobel went to get groceries, and he met Newton who was initially wary of him. The narrator rode a bike to the college where he logged onto his computer and saw how much of the hypothesis he had solved; it turned out to be a very important discovery. The narrator read the description of the Riemann hypothesis which the original Andrew had solved and he deleted the file.

The narrator looked through the original Andrew's emails and saw that he had forwarded his answer to the Riemann hypothesis to his colleague, Daniel Russell, an esteemed professor with a strong reputation. He realized that action needed to be taken and that he must follow a sequence. He deleted the email and attachment and put a virus into the computer so the discovery could not be found by anyone else. He saw a photo of Isobel and his son Gulliver and realized he was running out of time to follow the sequence. He was warned by the people from home to be like a prime number and strong in his mission. He returned home to find out more about his old character from Isobel and he met Gulliver. When Isobel went out to walk the dog the narrator tried to gain information from Gulliver who was angry with him for not being there for him.

The narrator read more books including some on poetry and tried to gain more information from Isobel over dinner. He received a call from Daniel which meant it was time to follow the sequence. The narrator went to the Russell house and after a brief conversation eliminated Daniel while making it look like he had a heart attack. He experienced remorse later and contemplated mortality for the first time. The narrator listened to some music later with Newton, healing him in order to gain his trust, and he saw Gulliver skipping school. He followed him to see him standing by the train tracks before returning home.

The narrator learned of an example of human humility through the story of Grigori Perelman who turned down a prestigious mathematical prize in favor of anonymity and a quiet life. The narrator and Newton bonded over food and Gulliver told the narrator not to tell Isobel about his having skipped school. Isobel came home and the narrator observed the grace with which she moved while entering the house. Isobel told him to phone his mother and he tried to find out if he had told his mother anything, which he had not. The narrator told the aliens from home that he had completed the mission and there was no need to eliminate Isobel and Gulliver; they said that someone else would be sent in his place.

The narrator prepared to eliminate Gulliver when the latter attacked the former in his sleep, with the narrator allowing him to. Isobel tended to his injuries when he felt pain for the first time. He understood for the first time why humans sought company in the dark. He asked for more time to complete the mission, saying that humans were more complex than they had thought. He found an unpublished novel by Isobel describing her current life at home. He was contacted by his friend Ari who indicated he knew a secret and the narrator thought he would have to take another life. He puzzled over how humans had not yet discovered immortality and that they acted in certain ways in order to cope. He went to a football match with Ari, from whom he found out that he had been having an affair with a student.

The narrator and Isobel went to Daniel's funeral where he admired Isobel's offer to help his widow. Later the narrator found a book he had written and experienced regret that he had destroyed humanity's chances at advancement. He went to give a lecture where he described the odds of finding extraterrestrial life, and the student, Maggie, approached him and started flirting. The narrator tried to tell Ari his secret at lunchtime but was prevented by extreme pain inflicted by the people from home. He told Isobel about Gulliver skipping school and realized he really did care. Later that night he found Gulliver on the roof attempting suicide and he saved his life. He realized the finality of death and acknowledged how he had done the opposite of his mission. The aliens from home told him he had been corrupted and the narrator agreed he had been.

Isobel reminded the narrator that he had never really been there for Gulliver but that he had done a great thing the other night saving his life. He manipulated the online accounts of those who had been bullying Gulliver. The narrator and Gulliver took Newton for a walk and encountered his bully, and the narrator told Gulliver to fight back. The narrator saved Isobel from being taken by the aliens from home and appreciated her fully for the first time. The narrator asked to be made human and was granted his wish from the aliens from home, disconnecting him and leaving him alone. The narrator realized what it meant to be fully human for the first time, struggling with all the small difficulties of the daily routine.

The narrator and Isobel enjoyed a pleasant evening together with wine, and the next day while hung over he saw a stranger lurking outside the house who then ran away. Isobel began to notice how different her husband had become and the narrator was on the verge of telling the truth but decided not to yet. Later that night there was an intruder who had been on Isobel's computer, and they tried to forget about it by going to the theater and bonding all over again. They faced Zoe and her new boyfriend on the way home who attacked the narrator, leaving him in severe pain. He realized in hospital that he would one day have to tell his family who he really was, and when he returned to work he was invited to the pub by Maggie. They had a few drinks and went back to her place but he ended up going home. He told Isobel about Maggie who was furious and kicked him out, making him realize the seriousness of what he had done.

The narrator got drunk and sat with a homeless man on a park bench, who had seen a downturn in his own fortune. They talked for a while then he received a call telling him that Ari was dead. He ran home and realized that a replacement had been sent to carry out his mission and that was who had intruded the other night. He encountered the replacement who told him that he had become just like the humans. The narrator pretended to go along with the plan and told him what Gulliver would be doing; he then hid while the replacement posed as him. The replacement started to manipulate Gulliver's mind but the narrator started playing the radio in order to thwart the process. Gulliver snapped out of it and stabbed the replacement.

The replacement died and the narrator burned his hand on a hot plate in order to make it look like it had all happened to him. He told Gulliver and Isobel his true identity and Isobel started mourning for her real husband. The narrator realized he had to leave but typed some life advice for Gulliver on his computer before going. He went to teach at Stanford University and traveled the world but started to miss his family; he returned home when invited to give a lecture at Cambridge. He turned Maggie down and saw Isobel, who gave money to the homeless man who he had met on the park bench. He realized that he loved her and that he was fully human now because all he wanted was to go home to live with his family again. Upon this realization he started walking back to the Martin home.