Many consider this series to be Blyton's best. I don't disagree, but I do think the Adventure series warrants more attention than it gets. The Five Find-Outers are far better than the Famous Five. The Famous Five tend towards arrogance and blind luck. The Five Find-Outers, on the other hand, go about things with a little more method.
Fatty, the leader from the second book onwards, intends to be a detective one day and it is from him that the children get most of their method and their good ideas. Larry and Pip are the other boys in the group and while Fatty is off disguising himself and being ingenious, these two tend to take on the more routine aspects of the investigations. Along with wandering around in the dark, of course.
Daisy and Bets are Larry and Pip's sisters and they join the boys in the interviewing of suspects, witnesses and the finding of clues. Bets, the youngest of the five, has a talent for solving the mystery by accidentally saying or noticing something that leads Fatty to the answer. Buster, the dog, is a Scottie that belongs to Fatty and loves nothing more than to have a go at the team's nemesis, Mr Goon.
Theophilus Goon is the local policeman, a bumbling idiot who is always taken in by Fatty's disguises and, no matter how hard
he works, is always outshone by the children. As an adult one feels rather sorry for Mr Goon, as the children star in front of his boss, Inspector Jenks, even though they lay false clues and interfere with Goon's investigations. They even waste police time by creating non-existent mysteries for Goon to investigate. He's a fantastic nemesis for the children, but a rather pathetic figure from the point of view of an adult reader.
This is one of Blyton's best series. You should read it.