The Five Find Outers and Dog Buster: The Five Find-outers (and Buster the Dog). The characters are:

• Frederick Algernon "Fatty" Trotteville – the leader of the Five Find-Outers from the third mystery on, when he justifies his leadership by demonstrating how to use invisible ink and how to escape from a locked room. He is given the nickname Fatty by the other children because of his initials, F.A.T. and his stout build. An only child, he receives generous amounts of pocket money from his parents and wealthy relatives. His wealth causes some friction with the other children, but Fatty is always willing to share his money with the group, often buying rounds of cakes, drinks and ice-creams. Fatty also uses his pocket money to finance his interest in disguises and stores a large collection of clothes, wigs, greasepaint, cheek-pads, false teeth and other items in his shed at the bottom of the garden. Although boastful by nature, he learns to be more modest as his bragging causes the other children to become irritated. Fatty is a skilled orator and poet, and able to create poetry ad-lib. He is apparently top of his form at his boarding school and his ambition when he grows up is to become a detective. Fatty develops an interest in ventriloquism as the series progresses. Bets in particular adores Fatty and is very loyal to him.
• Laurence "Larry" Daykin – the eldest of the five and the original leader of the Five Find-Outers, passing the role to Fatty at the beginning of the third mystery. Larry is sometimes irritated by Fatty's boasting. He is Daisy's older brother. He is the first character to be introduced in the series, but is developed considerably less than the other main characters as the series continues.
• Margaret "Daisy" Daykin – Larry's younger sister. Creating the Five Find-Outers was Daisy's idea. She is particularly good at thinking of plans and ideas.She is younger than Larry by a year and the same age as Pip and Fatty.
• Philip "Pip" Hilton – The same age as Daisy and a few years older than Bets, his younger sister whom he frequently teases. In contrast to Fatty's rather relaxed parents, Mr and Mrs Hilton are quite strict and often take a dim view of Pip and Bets's sleuthing activities, wishing that Pip especially would direct the same amount of energy into his schoolwork. In The Mystery of the Hidden House the Hiltons forbid Pip and Bets from getting involved in mysteries.
• Elizabeth "Bets" Hilton – Pip's young sister, and the youngest of the Five Find-Outers. She adores and hero-worships Fatty and he is very fond of her - she is the only one of the group who actively encourages his boasting. Bets is only part of the gang because of Fatty, as the others don't particularly want her around. However, they underestimate her, as Bets proves herself to be a worthy member. She is often the first to spot vital clues, which sometimes lead to the solution of the mystery, and also tends to see through Fatty's disguises before anyone else. She also thought of the name 'Five Find-Outers and Dog'.
• Buster – Fatty's jet-black Scottish Terrier. He thinks the world of Fatty and his favourite pastime is to nip at Mr Goon's ankles. His favourite food is biscuits, spread with potted meat.

Police Force:

• Theophilus Goon, also known as Mr Goon and Clear-Orf – the village policeman, who is outwitted by the five children in every story. Mr Goon would dearly love promotion, but considers the children to be hindering him rather than helping. To chase them away he often tells them to "Clear Orf" (instead of clear off). Consequently, the children have given him the nickname "Clear-Orf". Whenever he is upset or frustrated, Mr Goon constantly yells, "Gah!" causing much amusement among the children.
• Inspector Jenks, also known as Chief Inspector and Superintendent – the head of the local police department. Because the Five are resented by Mr Goon, the children always telephone the Inspector when they have solved a mystery. Over the course of the books he becomes a great friend of the children. Jenks is based on a real character from Blyton's home town who was promoted through the ranks of the police just as was his fictional counterpart. He becomes acquainted with the Five Find-Outers quite by chance in the first book of the series, The Mystery of the Burnt Cottage, while fishing. He admires the children, especially Fatty, much to the dismay of Mr. Goon, and clearly hints that he would like Fatty to become a policeman when he is grown up.He is also very fond of Bets who in turn looks forward to meeting him.

Minor characters:

• Ernest "Ern" Goon – Mr Goon's nephew. Ern is introduced in the book The Mystery of the Hidden House. Ern is a great lover of poetry, or "portry" as he calls it, though he never finished any poem (or 'pome' as he calls it) but Fatty can always finish it for him. That is one of the reasons that he is a great admirer of Fatty. Ern has twin brothers, Sid and Perce. Sid has a fondness for toffee, so much so that he has trouble speaking or being understood. At one time, Mr Goon scolded Sid for sucking stick-me-tight toffees in front of 'royalty'. (Actually just the Find-Outers in disguise.) In The Mystery of the Strange Messages, Ern reveals that Sid is now chewing gum instead. Ern might be considered to be an unofficial sixth member of the group, although class distinctions are maintained, e.g. Ern is not permitted to eat dinner with the children but instead eats in the kitchen with the Cook. He is also seen in The Mystery of the Banshee Towers and a few more books.