Trixie Belden is a series of 'girl detective' mysteries written between 1948 and 1986. The first six books were written by Julie Campbell Tatham. The following 33 titles were written by various in-house writers of Western Publishing under the pseudonym Kathryn Kenny. Between 2003 and 2006, Random House republished the first fifteen books of the series with new cover art illustrated by pulp artist Michael Koelsch. There has been no news of Random House publishing the remaining 24 books.

Original six written by Julie Campbell Tatham 1. The Secret of the Mansion (1948)

The book opens with thirteen-year-old Trixie begging her mother for a horse. Her two older brothers are away at camp for the summer, and Trixie is afraid she will be bored at their house, Crabapple Farm. The family cannot afford a horse, so Trixie is told she will have to save her money to buy one. She then sees a horse trailer outside a neighboring mansion. The Wheelers, a rich family from New York City, have just bought the mansion and are moving in with their teenaged daughter, Honey. Although tough Trixie thinks Honey is a sissy at first, they soon become fast friends. Trixie realizes that Honey is really a "poor little rich girl", her parents are never home, she has been very sickly, and she grew up at boarding schools, at camps, and with governesses. Trixie helps her new friend overcome these problems, while Honey balances Trixie's rash and impatient personality with her tactfulness and gentleness.

Recently, Trixie's neighbor on the other side was taken to the hospital with pneumonia. Trixie uses this chance to explore around the miser's rundown old mansion. Under the pretense of locking a window, Trixie and Honey climb inside to look around. They are shocked to find a tall, redheaded boy asleep on a mattress. The boy is Jim Frayne, the miser's 15-year-old great-nephew, who is running away from his abusive stepfather. The three become close friends, with the girls smuggling food to the mansion for Jim. Local legend says the old man hid his fortune in the house, electing to live in poverty after his beloved wife’s death. Honey and Jim are doubtful, but Trixie is sure the money is there somewhere if only they can find it before Jim's evil stepfather comes looking for him.

Eventually, Jonesy, the stepfather, does come after a newspaper article about an airplane crashing near the miser's mansion also features the news of the miser's death, the legend of the fortune, and a photo of a fireplace with Jim's silver christening mug on the mantle. Trixie finds the engagement ring that Jim's great-uncle gave his wife in a safe.

After Jonesy shows up, Trixie wakes up in the middle of the night and sees smoke from her window. The girls call the fire department and go to warn Jim. The mansion is burned almost to the ground, and Jim sleeps in the hidden summerhouse. When Trixie and Honey go there to the next morning to visit him, they find him gone and a note with the engagement ring in the summerhouse saying goodbye. He has run away again, this time in possession of some money he found hidden in the mattress he had been sleeping on.

The girls meet the great-uncle's lawyer, Mr. Rainsford, who tells them Jim's uncle set up a half-million dollar trust for him and that Jonesy will be replaced as the boy's guardian. He asks them to track Jim down.

2. The Red Trailer Mystery (1950)

Jim Frayne ran away at the end of The Secret of the Mansion, but later his great-uncle's lawyer showed up, revealing that Jim inherited half a million dollars and is going to be removed from his abusive stepfather's custody. Trixie and Honey set off in the Wheelers' trailer with Honey's governess Miss Trask to find their missing friend. They decide to check the boys' camps upstate since Jim mentioned getting a job there, but he always seems to be one step ahead of them.

On the trip, Trixie and Honey are faced with a strange and poor family in a luxurious trailer; the family's missing daughter; Mrs. Smith, a fat and motherly woman who's missing her locket; a trailer-robbing ring; and two suspicious workers at their trailer camp who may be involved. Trixie knows that the mysteries are tied together and the answer lies in the nearby forest.

At the end of the book, Honey's parents return. Honey runs to her mother and gives her a hug, something she has never done before. Her mother forgets her own shyness and hugs her daughter back. Jim is adopted by the Wheeler family, giving Honey an older brother. Jim tells Trixie that he is in charge now, but Trixie tells him to wait for her older brothers, Mart and Brian, to get back from camp.

3. The Gatehouse Mystery (1951).

The Gatehouse Mystery marks a point in the series when the hallmarks of the Trixie Belden books are solidly established. This book introduces Trixie's older brothers and marks the establishment of the "Bob-Whites of the Glen" club. The plot involves an adventure that follows when Trixie and Honey explore an old, abandoned gatehouse on the Wheelers' property which is to become their clubhouse.

4. The Mysterious Visitor (1954)

This book marks the entry of Diana (Di) Lynch and a man staying with her family who may or may not be her long-lost uncle. The end of this book foreshadows events that occur in The Mystery in Arizona.

5. The Mystery Off Glen Road (1956)

When the clubhouse is badly damaged, Brian uses the money he has been saving to buy a jalopy in order to purchase repair materials. To help him keep the car, Trixie wants to use the ring Jim gave her in the first volume as collateral. She also plans to get the Bob-Whites hired as temporary gamekeepers for Mr. Wheeler so that they can raise enough money to pay for the car. While they are patrolling, they come across the path of a mysterious poacher.

6. The Mystery in Arizona (1958)

Trixie, while at Di's "real" uncle's ranch, tries to find out what happened to Uncle Monty's employees when they mysteriously disappear.

Books written under the pseudonym Kathryn Kenny 7. The Mysterious Code (1961)

After the school district cracks down on secret clubs, Trixie and the other Bob-Whites put on an antique show to prove their worth. While collecting antiques, Trixie is robbed by thieves and finds a mysterious code in Honey's house. In the midst of this, romance blooms between Jim Frayne and Trixie Belden.

8. The Black Jacket Mystery (1961)

In The Black Jacket Mystery, a boy named Dan Mangan starts school in Sleepyside and lives with and works for Mr. Maypenny. Dan wears a black jacket that has a name on the back that has been painted over. Trixie is suspicious that Dan is a member of a gang and that he is up to no good.

9. The Happy Valley Mystery (1962)

In The Happy Valley Mystery, the Bob-Whites stay with the Beldens' Uncle Andrew on his sheep farm in Iowa. When Trixie learns that Uncle Andrew's sheep are being stolen by thieves, she is immediately on the hunt for the culprits. Trixie keeps accusing the wrong people of being thieves based only on how suspicious she thinks they look. All of the adults laugh at Trixie's exploits as she vows to solve the mystery.

10. The Marshland Mystery (1962)

Trixie wants to replace Miss Bennett's herb collection, which was destroyed by a clumsy student. Brian gives Trixie directions to Martin's Marsh. During the outing, Trixie and Honey meet Miss Rachel, who is the last of the Martins. Meanwhile, a child prodigy named Gaye is staying with the Wheelers. Gaye will be playing in a recital and has to practice constantly. Gaye is a snobbish young girl, and she is also very unhappy. Gaye also goes out to the marsh, and Gaye's adventure leads to complications for Miss Rachel, who may end up losing her home.

11. The Mystery at Bob-White Cave (1963)

In The Mystery at Bob-White Cave, the Bob-Whites stay in the Ozarks with the Beldens' Uncle Andrew. Trixie sees an article that advertises a $500 reward for the first person who can provide specimens of ghost fish in each of three different stages of evolution. Trixie is obsessed, so Uncle Andrew purchases the necessary equipment, and the Bob-Whites begin exploring the nearby caves.

12. The Mystery of the Blinking Eye (1963)

In The Mystery of the Blinking Eye, the Bob-Whites have a vacation in New York City with their friends from Iowa. Trixie helps a woman at the airport, and the woman writes a strange verse in Spanish. Miss Trask translates the verse, which strangely rhymes in English. Trixie is soon convinced that the verse predicts the future, and all of the Bob-Whites' New York adventures follow the verse as strange men follow them around and try to steal Trixie's purse.

13. The Mystery on Cobbett's Island (1964)

In The Mystery on Cobbett's Island, the Bob-Whites stay on Cobbett's Island in a home rented by the Wheelers. Trixie finds an old letter in a book, and the letter indicates that following the directions in a sailing game will lead to some money that has been hidden on the island. Trixie unearths several clues which reveal who the rightful owner of the money is, and that person could well use it. The Bob-Whites hope that they can find the money and bring happiness to others.

14. The Mystery of the Emeralds (1965)

In The Mystery of the Emeralds, Trixie discovers a hidden room in the attic at Crabapple Farm. In an article of clothing, she discovers a letter. Some excellent sleuthing leads to an elderly woman who lets Trixie and Honey read some diaries. The girls discover that the letter is a clue to hidden emeralds on an estate near Williamsburg. Fortunately, the Bob-Whites are able to travel with the Lynches to Williamsburg so that they can pursue the quest.

15. The Mystery on the Mississippi (1965)

In The Mystery on the Mississippi, the Bob-Whites travel to St. Louis, where Trixie discovers a mystery immediately. Trixie finds papers in the wastebasket of her motel room. Later, she learns that a man was looking for some papers, but she keeps them. This starts a sequence of events where three people stay in constant pursuit of the Bob-Whites and try to kill Trixie. Even when the authorities learn about the case and warn Trixie away from it, she continues her investigation with no thought for her own safety.

16. The Mystery of the Missing Heiress (1970)

Jim discovers that he has a cousin, Juliana, who will inherit $150,000 from the sale of some land on the Hudson River. When Juliana arrives, she is a bit distant and wants to close the sale of the land as quickly as possible. Meanwhile, a girl was struck by an automobile on Glen Road. The girl has amnesia, and everyone calls her Janie. The Beldens have Janie come home to stay with them, and Trixie tries to figure out who Janie really is.

17. The Mystery of the Uninvited Guest (1977)

In The Mystery of the Uninvited Guest, Trixie's cousin, Hallie, comes to visit, and Trixie is furious. Trixie and Hallie have never gotten along, and Trixie takes offense at everything Hallie does. Meanwhile, Bobby acts strangely, talking about a wheelchair that only he saw on Glen Road, and food keeps disappearing out of the Beldens' kitchen. As Trixie tries to puzzle out the mysterious events, she helps the Wheelers plan the wedding of Jim's cousin, Juliana.

18. The Mystery of the Phantom Grasshopper (1977)

In The Mystery of the Phantom Grasshopper, Hoppy the weather vane disappears from its perch above city hall. Trixie has always loved the weather vane and is upset that it has vanished. Later, a valuable coin collection also vanishes from a school classroom. Trixie fears that Miss Lawler and her friend, Sammy, may be responsible for the coin theft. Trixie really likes Miss Lawler and fears that she is guilty.

19. The Secret of the Unseen Treasure (1977)