Each chapter describes an adventure in Rose's life as she learns to help herself and others make good choices. Rose must define for herself her role as the only woman of her generation in her family and as an heiress in Boston's elite society.

Motherless for most of her life, 13-year-old Rose looks to her many aunts, her friends, and the housemaid Phebe as feminine role models. At the same time, she is suddenly confronted with a male guardian and seven male cousins, none of whom she knows well, after losing her beloved father, the only man in her life.

Like all of Alcott's books for young people, the story takes a high moral tone. Various chapters illustrate the evils of cigar-smoking, "yellow-back" novels, high fashion, billiards, and patent nostrums, while promoting exercise, a healthy diet, and wholesome experiences of many kinds for girls as well as boys. Alcott uses the novel to promote education theories many of which appear in her other books. For example, in choosing Rose's wardrobe, Uncle Alec rejects current women's fashions (such as corsets, high heels, veils, and bustles) in favor of less restrictive, healthier clothing. Although he discourages her from the professional study of medicine, he educates her in physiology, a subject her aunts consider inappropriate for girls, so she can understand and take charge of her own health. Rose is prepared for a career as a wife and mother, yet is taught that she must take active, thoughtful control of her fortune so she can use it and social position to the best advantage of the larger community. Written in an age when few women had control of their own money, property, or destinies, Alcott's portrayal of Rose's upbringing is a good deal more revolutionary than 21st-century readers may realize.

The sequel to Eight Cousins is Rose in Bloom (1876), which continues Rose's story into young adulthood, depicting courtship and marriage, poverty and charity, transcendental poetry and prose, and illness and death among her family and friends.

Chapter One, "Two Girls": Rose Campbell is in the best-parlor, where she sits, mourning her father's death. She hears what she thinks is a bird-song, and follows it to the kitchen, where she sees Phebe Moore washing dishes. Rose asks Phebe what bird might have been twittering the songs (which were of several different birds) and Phebe answers a "Phebe-bird". Phebe then says it was really her doing the bird-songs, and does several for Rose, before Dolly, the cook (Debby in some editions) comes in, and says that there are some people to see her. Rose sees what she thinks is a "circus" and then goes out into the front room of the house.

Chapter Two, "The Clan": Rose beholds her several boy cousins in the front room. At first she is afraid, because she thinks boys to be "a sort of wild animal" but tries to remain calm, and soon finds out she is very wrong. Archie, the eldest, introduces him to the others, (listed by age), Charlie, Mac, Steve, Will, Geordie, and Jamie. Mac abruptly asks Rose if she has any books, and, when Rose answers yes, he immediately goes off to read them. The talk goes on, and the boys go outside to show her what her "circus" really was - their new ponies and cart. A little afterward, Dolly calls them in for tea, which Aunt Plenty makes, each boy telling her different things to make. After tea, Rose goes upstairs and reads to Aunt Peace. A few minutes after she has gone to bed, Rose wakes up to see Uncle Alec over her.

Chapter Three, "Uncles": Waking up the next morning, Rose sees Uncle Alec walking up from the sea, which is apparently very near their house. She calls out to him, and he climbs up the column by her window to her balcony, and thereby entering her room. They converse for a while, Alec (who is a doctor) saying he shall take charge of her health from now on, and throwing the nostrums which Aunt Myra has given Rose out the window. When Phebe brings Rose a cup of coffee, Alec also throws this out the window, and tells Phebe to bring up two glasses of fresh milk instead. At breakfast, Alec manages to get Rose to eat oatmeal, a dish she "detests", and then, at tea, he takes a slice of brown bread, rolls some up into little balls, and puts them in a medicine-bottle, to give to Rose if any of the aunts think she should have physical medicine. Later the boys are very surprised in church to see Uncle Alec.

Chapter Four, "Aunts": Uncle Alec is talking with the aunts, all who have different dispositions. Aunt Jane thinks that Rose should have been kept in Miss Power's boarding-school, Aunt Clara thinks she should be put in a finishing-school for a year and then sent into society, Aunt Myra thinks Rose will die, and Aunt Jessie agrees with Alec. After Uncle Mac makes a comment that Uncle Alec ought not to marry because there are already too many women in the family, both uncles "hastily withdraw".

Chapter Five, "A Belt and a Box": Uncle Alec and Rose go out early in the morning to milk the cow, and afterward Alec tells Rose to run around the garden, which she does, and Alec then tells her that her belt is too tight. It becomes apparent that Rose is somewhat vain (she even confesses it), for she does not wish to loosen it, which Alec does anyway. Then he tells Rose he has got a box of things for her upstairs in Aunt Peace's room, and Rose goes to examine the things (mostly clothing Alec has picked up on his travels, which much differ from the fashions of Alcott's day), while Alec "turns the house upside down" furnishing his new room. Then Rose decides to give Phebe some of the things, and "adopt" her, though Peace tells her she cannot legally do this until she is older. Later they go see the Aunts, and give the boys some of the things out of Alec's many boxes.

Chapter Six, "Uncle Alec's Room": Alec reveals that the room he has been furnishing is for Rose.

Chapter Seven, "A Trip to China": Rose and Alec go out in Alec's new boat, though Rose confesses she is rather afraid of it. They go to Uncle Mac's dock, where he is on a ship trading with two Chinese gentleman, Whang Lo and Fun See. Fun See entertains Rose with some Chinese things he has brought from China, and later, going back from Uncle Mac's warehouse, Rose and Alec meet the boys' boat, and race back to the Campbells'.

Chapter Eight, "And What Came of It": Rose and Uncle Alec are in a room, and Rose is reading Alec some things out of one of Charles Dickens' novels, when Aunt Jane comes in. Rose bewilders Jane by telling her all the things she has learnt from Uncle Mac and the Chinese gentlemen about China.

Chapter Nine, "Phebe's Secret": Phebe tells Rose she has a secret, which turns out that the boys are going to do some special fireworks on the "Island" on the fourth of July. Alec suggests he and Rose take the boat over to the "Island", which they do, and find the boys camping there. Alec reveals that he and Rose will camp with the boys until the Fourth of July, and Alcott goes on to describe it.

Chapter Ten, "Rose's Sacrifice": Rose determines to make a sacrifice for Phebe. She leaves a note for Alec, goes back to the house, sends Phebe to the "Island" to enjoy the last day of the camping-trip, and does Phebe's work for the day. At the end of the day, Rose rows out in a boat with Uncle Mac to watch the boys' special fireworks - which show several Scotch thorns, representing the boys, around a rose.

Chapter Eleven, "Poor Mac": Mac, from studying outside all day on the camping-trip, gets a sunstroke. After this, his eyes give out from his reading with his nearsighted eyes without bothering to get glasses. He is consigned to a dark room for a long time, and forbidden to read, so Rose reads to him. One day he asks her how long it will be until he can go to school again. She answers a year, at least, and he says he should be in college by then. He then asks if his eyes are getting worse, and she answers that they are, and if he is not careful, he will go blind, "...the word 'blind' seemed to have knocked him down, for he had buried his face in the pillow, and lay so still that Rose was frightened.". After some more conversation, she sings him a song (an old Scottish ballad, "The Birks of Aberfeldie"), which sends him to sleep.

Chapter Twelve, " 'The Other Fellows' ": Rose goes out, and, coming back, discovers the other boys in Mac's dark room, practically turning it upside down, while Mac argues with his brother (Steve). Rose demands the boys to leave, and later they apologize and decide to try to help Mac more.

Chapter Thirteen, "Cosey Corner": Mac, though slightly recovered, is still condemned to idleness, and growing bored, he says to Rose " 'Look here, if you don't invent some new employment or amusement for me, I shall knock myself on the head as sure as you live.' " So Alec decides to take them up to the mountain village of Cosey Corner, to stay at Mother Atkinson's, with Aunt Jessie and Jamie. Alcott then goes on to describe their trip at Cosey Corner, and "The Cosey Corner Light Infantry", in which Jamie is already a "Colonel", and when its "highest-ranking officer", "Captain" Dove, tries to do a sermon as an army chaplain in an old, dilapidated church, and how everyone disrupts it.

Chapter Fourteen, "A Happy Birthday": It is Rose's birthday, and she sees Uncle Alec coming out of a carriage, and so, to surprise him, she tries to ride the horse, "Barkis", up to him, but she falls off. Later Jamie, Pokey (a friend of Jamie's), "The Cosey Corner Light Infantry", and Mac, put on a series of sketches for Rose on a makeshift stage out by Mother Atkinson's. Later they find out Rose's injury falling off "Barkis" was more serious than they thought, and she has sprained her ankle very badly.

Chapter Fifteen, "Ear-Rings": Rose succumbs to her vanity, and lets Annabel Bliss pierce her ears.

Chapter Sixteen, "Bread and Button-Holes": Alec recommends that Rose learn to bake bread from Aunt Plenty, which she does; afterward learning to sew from Aunt Peace.

Chapter Seventeen, "Good Bargains": Rose manages to get Charlie and Archie to stop smoking, and Geordie and Will to stop reading "yellow-back" novels.

Chapter Eighteen, "Fashion and Physiology": Aunt Clara has convinced Rose to put on a dress of her kind of fashion, in which Rose is very awkward, and so Alec gets a better one of his style; afterward Alec announces he is going to teach Rose physiology.

Chapter Nineteen, "Brother Bones": Rose teaches Aunt Myra about bones, and then Alec tells the boys a story about the skeleton used for studying ("Brother Bones").

Chapter Twenty, "Under the Mistletoe": It is Christmas, and Phebe and Rose give each other presents; and then later everyone eats Christmas dinner, and then Uncle Jem, Archie's father, comes for a visit after being at sea for years. Afterward the boys try to get her to kiss "old Mac" under the mistletoe, and she does it of Uncle Mac, instead of Mac!

Chapter Twenty-One, "A Scare": Rose waits outside for Mac, who is stuck at home, and contracts a very serious cold. When Charlie finds out it is Mac's fault, he goes to Mac's to "blow him up", as he terms it. "He did it so energetically and thoroughly that [Mac] was cast into the depths of remorseful despair, and went to bed that evening feeling that he was an outcast from among men, and bore the mark of Cain upon his brow.". Mac visits Rose in her room in the middle of the night and begs for forgiveness, which she laughingly grants, and then he stumbles downstairs and falls asleep on the sofa.

Chapter Twenty-Two, "Some-Thing to Do": Rose gives Phebe some schooling.

Chapter Twenty-Three, "Peace-Making": Archie and Charlie have an argument, and Rose resolves it.

Chapter Twenty-Four, "Which?": Alec invites the aunts to tea, and reveals that his "experiment" (as he terms his trying to help Rose's health) is over, and, as he promised a year ago, he would let Rose choose who she wants to stay with for the next year. Rose then comes in with the boys, and, finding out what is going on, each one entreats her to stay with them for the next year, and the aunts do the same. Rose finally picks Uncle Alec.

Rose Campbell: The central character of the novel is the daughter of the recently deceased George Campbell, one of six Campbell brothers who are nephews of Aunts Plenty and Peace Campbell. She is heiress to his considerable fortune. (The Campbells, wealthy residents of Boston, are of Scottish descent, and some of them are engaged in the China trade.) Rose, 13 1/2 at the beginning of the novel, is a pretty and sweet-natured child without marked talents of any kind. She has never known her mother and has lived apart from the rest of the Campbell family all her life. As the story opens, she is mourning the death of her father and awaiting with apprehension the arrival of her unknown guardian, Alec Campbell. She speaks French fairly well, and is slightly vain (as becomes apparent when her uncle wishes her to refrain from the wearing of tight belts around her waist).

The aunts of the "Aunt-hill" edit

• Plenty Campbell: Maiden great-aunt of Rose and matriarch of the family. Aunt Plenty is chatelaine of the ancestral home in Boston, which is "a capital old mansion … full of all manner of odd nooks, charming rooms, and mysterious passages. Windows broke out in unexpected places, little balconies overhung the garden most romantically, and there was a long upper hall full of curiosities from all parts of the world … "
• Peace Campbell: Maiden sister of Plenty. An invalid, she has a tragic history. Her lover died hours before their wedding, and "gentle Peace" never recovered from the blow. Universally beloved by the family, she is the Mary to Aunt Plenty's Martha.
• Myra Campbell: She is a widow and we never learn her husband's name. Myra is a gloomy, self-absorbed hypochondriac, obsessed with medicines and mortality. Her presence is tolerated rather than welcomed by the rest of the family. She is the mother of the only other female Campbell cousin, Caroline, who died young – possibly "dosed to death" – inadvertently poisoned with "quack medicines" by her mother.
• Jane Humphries Campbell: Wife of Uncle Mac and mother of Rose's cousins Mac and Steve. Aunt Jane is a stern disciplinarian, utterly lacking a sense of humor. But she is completely reliable. Her bark is worse than her bite, and Rose comes to like and trust her.
• Clara Campbell: Wife of Uncle Stephen, who is absent in India. Clara is a social butterfly, completely absorbed in Boston's high society. She looks forward to sponsoring Rose's debut in a few years’ time and secretly plans that Rose shall marry her son Charlie.
• Jessie Campbell: Wife of Uncle Jem, a sea captain. Jessie has raised four sons – Archie, Will, Geordie, Jamie – almost without the assistance of her husband, who is always away at sea. Steady, wise, and loving, Jessie is Rose's favorite aunt and the nearest substitute she has to a mother. Jessie is the aunt most trusted by Rose's guardian, Uncle Alec.

The Campbell brothers, uncles of Rose and nephews of Aunts Peace and Plenty edit

• Alec: The principal male character. A seafaring doctor, he became Rose's guardian when her father George died. He has never married; we are led to assume that the great love of his life was Rose's mother, who chose to marry George. Alec has "advanced" ideas about child-rearing, which he implements in so gentle and loving a fashion that Rose is restored to health and happiness in spite of her fears. The aunts are nervous about (or even opposed to) some of Alec's ideas, but they come to trust him implicitly.
• Mac: Married to Jane and father to Rose's cousins Mac and Steve. He is engaged in the China trade and has a warehouse on the Bay full of Asian treasures. A trifle henpecked by his masterful wife, he spends most of his time in his counting-house. He is very fond of Rose and secretly hopes that she will marry one of his sons.
• Jem (James): Married to Jessie and father to Rose's cousins Archie, Will, Geordie, and Jamie. Jem is a sea captain who makes a surprise appearance toward the end of the book.
• Stephen: Married to Clara and father to Rose's cousin Charlie. His profession is never specified. He lives in India, perhaps driven from home by his distaste for Clara's propensity for high society. Stephen never makes an appearance in Eight Cousins.
• George: Recently deceased father of Rose, for whom she grieves deeply. Uncle Alec and he "fell out" because they loved the same woman. Years later they met and made up, and George asked Alec to look after Rose if anything happened to him.

A sixth brother-in-law, Aunt Myra's deceased husband, is never named.

The Campbell cousins, in order of age edit

• Archibald (Archie): Eldest son of Jem and Jessie. Eldest of all the cousins at age 16, of steady and thoughtful character, he is the Chief, much respected by all the boys and an "older brother" figure to Rose.
• Charles C. (Charlie): Also known as Prince Charlie, the "flower of the family," considered the most handsome, talented, and promising of the lot. Age 16. He is the spoiled only child of Stephen and Clara—spoiled by his too-indulgent mother, with no father present to give him guidance. Charlie and Archie are inseparable friends and lead the way in all exploits.
• Alexander Mackenzie (Mac): Elder son of Mac and Jane. Age 15. Known as the Bookworm, or simply "the Worm," Mac always has his nose in a book and is regarded as the wisest and most learned of the cousins, although deficient in basic social skills through absent-mindedness and lack of interest.
• Stephen (Steve): Mac's younger brother. Age 14. A good-natured though rather conceited dandy, he idolizes Charlie and copies him in everything, not always to his own advantage.
• William (Will): Jem and Jessie's second son. Age 12.
• George (Geordie): Jem and Jessie's third son. Age 11.
• James (Jamie): Jem and Jessie's youngest. Age 6. Much-loved but unspoiled.

Other characters edit

• Phebe Moore: Housemaid of Aunts Plenty and Peace, a girl from the poor house, who is employed on trial at the opening of the story. Lonely Rose befriends Phebe and then "adopts" her as a sister, teaches her improvements in reading and writing skills, admires Phebe's marked musical talent and upright character, and includes her in all aspects of her life as Phebe becomes her personal maid. (At a time in our social history when it was unusual for members of a wealthy household to develop close personal relationships with "the help," this is a testament to the sweetness of Rose's unspoiled character.)
• Debbie: Bad-tempered but good-hearted cook in Aunt Plenty's household.
• Annabelle Bliss: Friend of Rose. She is "the model child of the neighborhood," daughter of a prominent Boston family whom the aunts consider suitable for Rose to know; however Rose can't bear her. Alcott frequently satirized fashionable, empty-headed girls in her novels.
• Mother Atkinson: Kindly doyenne of the wholesome mountain household (location unspecified, but probably in Maine or New Hampshire), known as Cosey Corner, where Rose and various family members spend several memorable summers.
• Fun See: A Chinese boy who has come to America to be educated in a western school.
• Whang Lo: An elderly Chinese merchant who does business with Uncle Mac Campbell; he wears Western dress and speaks good English.

The Alcotts themselves would summer in a location called "Happy Corner" in Walpole, New Hampshire, but the description of "Cosy Corner" places it within walking distance of Mount Washington, very likely in Intervale. In the 19th century, New Englanders who could afford it went to the mountains or the seashore for the fresher, cooler air considered sovereign for physical and mental complaints.

• Eight Cousins at Project Gutenberg
• PDF scan of Eight Cousins
•   Eight Cousins public domain audiobook at LibriVox
• Louisa May Alcott official website