The youngest daughter and middle child of the Mortmain family. The book's narrator, she is perceptive, thoughtful, and frequently witty. As a teen on the cusp of womanhood, she attempts to manage her family's tempestuous and eccentric troubles while sorting out with her own first experience with romantic love.
- BookWorm: Loves to read.
- Daddy's Girl: She wants to be a writer, much like her father. But she is slowly losing respect for her father with very good reason.
- Drowning My Sorrows: When she realizes that she is in love with Simon, Cassandra runs to the pub to have a few glasses—only to be put off by the price.
- Impoverished Patrician: Much like the rest of her family.
- In Harmony with Nature: She loves every single season and takes great comfort in all the beauty that surrounds her home.
- The Narrator: Everything in the book is from her point of view.
- Nice Girl: Not only she can put up with Rose's tantrums with kind words and smiles but she also is very kind to their pets and is discomfited by the idea of furs.
- Love Hurts: Boy does it ever when the guy you are in love with is going to marry your Gold Digger sister.
- Middle Child Syndrome: Averted. If anything, Cassandra is the most sensible and reliable of the three children, and both her father and stepmother recognize these traits.
- Writers Are Writers: She spends the book honing her writing skills.
- Smitten Teenage Girl: She falls in love with Simon.
- Zany Scheme: She formulates a plan to get her father writing again with the help of her younger brother Thomas. It involves imprisoning him in an isolated tower for a few days.
The eldest child of the family, extremely beautiful, hot-headed, and prone to dramatics, she turns out to be surprisingly steely and pragmatic as she schemes to marry into money to rescue herself and her family from their crushing poverty. She and Cassandra are particularly close and Rose shares all her secrets except one with her sister.
- Country Mouse: Has no idea how to flirt. When the Cottons come to visit the second time her blatant and over the top flirting causes them to basically blacklist the Mortmains.
- Distracted by the Luxury: Once she gets engaged all she talks about in her letters to Cassandra is her new clothes and furnishings. Especially her peach colored towels.
- Gold Digger: A somewhat justified example, depending from the point of view.
- Fiery Redhead: Slapped Neal Cotton when he nearly humiliates her.
- Like Father, Like Daughter: While unremarked upon in the books, Rose's explosive temper, her tendency toward loud, angry declarations, and her stubbornness, is all very much like her father. (Rose's red hair is also very distinctive and in the few descriptions we have of him, Mortmain's hair is described as "thin and gingery," implying they may look alike as well.)
- Redhead In Green: Is well aware of this trope. In one scene she orders a creme de menthe, a drink she hates, because of the green drink's contrast with her hair.
The youngest child of the Mortmain family and the only son. Probably the most book-smart of the trio, with a keen interest in science and astronomy, he attends school on a scholarship and is "perpetually underfed." Until the third act, he lingers in the background and seems to take a hands-off view of his sisters' antics, although he is perceptive enough to be suspicious of Rose's real feelings toward Simon.
- Child Prodigy: Goes to school on a full scholarship and has a keen interest in science and engineering. Also his tastes in literature and art are very highbrow: Cassandra is astonished to realize that Thomas understands their father's work much better than she does.
- Cheerful Child: He is actually fifteen but the characterization fits him.
- Hidden Depths: He bears poverty much better than his older sister Rose. For as little as he directly interacts with the rest of the plot, it turns out that he's been paying attention all along and has some very sharp, insightful perceptions on everyone else's predicaments.
- Good Cop/Bad Cop: When he and Cassandra imprison their father in the Belmotte tower he has to take the Bad Cop role since Cassandra is a little too softhearted.
An artist's model and the stepmother of the Mortmain children, she is genuinely kind and supportive, but also tends to be dramatic and put on deliberate poses in order to satisfy her artistic temperament. She is devoted to Mortmain, pinning most of her own artistic inspirations on being his "muse" to inspire him to write a second novel, to the point that she had sacrificed her own connections in the artistic world to live with him in poverty. She is also fond of all the children and schemes along with Cassandra to help further Rose's prospects.
- Cloudcuckoolander: Boy is she ever. Prone to strange strange, grandiose statements and communing nude with nature.
- Christmas Cake: At the advanced age of almost thirty, Topaz worries that her best years are behind her.
- Giftedly Bad: Her painting of the Belmotte tower was atrocious.
- In Harmony with Nature: Communing with nature is something she is deeply passionate about.
- Hidden Depths: When the Cottons first started to visit she downplayed her looks and engaging personality as not to detract attention from Rose. She also is very practical when she needs to be.
- Manic Pixie Dream Girl: Definitely.
- The Muse: Topaz has a desperate romantic attraction to art and the world of artists, but has no talent of her own except the ability to inspire others to create. She's pinned her hopes on inspiring Mortmain to his next masterpiece.
- Wicked Stepmother: Thoroughly averted. She genuinely loves her stepchildren (even through her rocky relationship with Rose) and does her best to be a homemaker and supportive wife even with extremely limited resources.
- Ugly Guy, Hot Wife: The hot wife in question.
The patriarch of the family. A temperamental author with one masterpiece to his name, he has had writer's block for more than a decade and much of his fierce temper and reclusiveness seems to stem from his guilt at having failed them as a father and husband, as well as failing himself as a writer.
- Abuse Mistake: The cake knife incident was far less serious than it looked to the neighbor.
- Abusive Parents: Maybe not by the standards of his time, but nowadays he could rightly be accused of holding his entire family hostage with his hot temper. He frequently explodes verbally at his family, causing them to walk on eggshells to keep from setting him off. On two occasions, he physically attacks Cassandra, and he frequently hurts her by insulting her writing and intelligence. Not to mention his neglect of Topaz, his refusal to support an entire household of people who can't afford food or clothes (or rent), and the cake-knife incident.
- Brilliant, but Lazy: People allow James to cost on the success of his first book on the assumption that he will invariably produce another. Instead, he's spent the past ten years reading mystery novels and doing crosswords.
- True Art Is Incomprehensible: Applies to both his first work (which is so densely symbolic and experimental that few people know what the heck it's about) and to the man himself. People think he's a genius on a level that no one can truly understand, so all of his eccentricities are tolerated as part of his "creative process"—even when he starts digging fishbones out of the trash.
The former maid's orphan who is like another son to the family. Except he is not.
- Bishōnen: Leda Fox-Cotton describes him as being beautiful yet still masculine. Topaz says that in her younger days she would have been unable to resist him for a minute. And Ivy Stebbings has her eye on him.
- Dogged Nice Guy: To Cassandra, too bad that she does not feel the same.
- I Want My Beloved to Be Happy: He is the one that reunites Rose with Neal by informing the latter that Rose loves him. Too bad that it did not result in Cassandra getting her love.
- Love Hurts: Poor Stephen.
Simon CottonThe eldest Cotton brother and the heir of Scoatney Hall. Separated from his brother by their parents' divorce, he was raised in New England by his mother and moved in academic and intellectual circles. Falls in love with Rose but has a deep, respectful friendship with Cassandra.
- Foreign Culture Fetish: Loves everything about England and is enamored with the idea of being real landed gentry, to the point that he starts developing a slight English accent.
- Love Makes You Dumb: He's too smitten with Rose to notice anything else...including the fact that she doesn't love him back.
- Sibling Yin-Yang: With his brother Neil. Simon is the more thoughtful, romantic, and sensitive of the pair.
Neil CottonThe younger Cotton brother, he was raised in California by his father and is a rugged, earnest, independent outdoorsman who dislikes England and can't wait to go back to his ranch in America. He, too, falls in love with Rose, but keeps his affection secret...until he can't anymore.
- Bad Ass Boast: Convinces an entire crowd of strangers that not only did a bear exist (in the middle of Suffolk), but that he wrestled it into submission before stabbing it with a pitchfork.
- Don't Split Us Up: Neil resents Rose, fearing that if Simon falls in love with her, Simon will never leave England. After being separated for fourteen years by their parents' divorce, Neil is very sensitive about losing his brother again making it all the more difficult to admit his feelings for Rose, since it amounts to breaking up his own brother's engagement.
- First Girl Wins First Boy Wins: Secretly beats Simon to the punch with Rose.
- Sibling Yin-Yang: With his brother Simon. Neil is the more temperamental, but also the more pragmatic, fun-loving, and easy-going of the pair.
Mrs. Elsbeth CottonNeil and Simon's American mother. She is independently wealthy, incisive, and extremely intellectual, with a keen interest in literary circles. She, too, is interested in reviving Mortmain's sagging career.
- Adaptational Personality Change: In the film, she makes several snide remarks implying that she thinks of Rose as a golddigger and that has generally low opinions of the rest of the Mortmains, too. In the book, however, she calls Rose the daughter she never had and seems to regard the Mortmains fondly, going out of her way to both assist and include them. In particular, in the film, at Rose's wedding to Neil, Mrs. Cotton looks as if she's going to tear out Rose's hair, while in the book she seems equally upset with Neil and is more disappointed and confused than angry at the outcome.
- Brutally Honest: Often to the point of seeming rude, but it's also a pretty effective method of getting people to open up.
- Doting Parent: To both her sons, then extends the offer to Rose when she gets engaged to Simon.
Aubrey Fox-CottonA distant relation to the Cotton family, he plays a very small part in the novel but is involved in the London art scene, which helps him bond with Topaz.
- And the Rest: Aubrey largely disappears after the dinner party at Scoatney.
- Strictly Professional Relationship: With Topaz, though Cassandra worries it might be otherwise, particularly when his efforts to reintroduce Topaz to the art world makes Topaz consider leaving Mortmain.
Leda Fox-CottonWife of Aubrey and likewise a distant relative of the Cottons, she is a professional photographer and a bit of a vamp with a predatory eye for handsome new talent...including Stephen.
- It's Not Porn, It's Art: Her entire studio is full of photographs of nude men, some blown up to terrifying sizes.
- Mrs. Robinson: It's hinted that Stephen isn't the only handsome young model she's seduced.
- The Vamp: Has some tendencies toward this, and certainly looks the part in the film, right down to the Theda Bara haircut.