The Woodstock Irregulars is a young boys adventure mystery series. It takes place in the early 1960s in a little town in Wisconsin. Slim Lorens and Dean Brewster see suspicious activity in an abandoned house in the little village of Woodstock. Further investigation leads them to believe the intruders might be wanted by the FBI, but first they have to find evidence of who they are and what they are doing, which leads to trouble and danger for the boys. They engage the help of two of their schoolmates, Arlen Bailey and Danny Black, to form "The Woodstock Irregulars" detective agency to give the law a hand, as soon as they can escape!

This series tells the story of friends Slim Lorens and Dean Brewster from the ages of approximately 10 to 14. Slim is the voice of the series, which is written in first person. Slim has an active imagination, seeing mysteries everywhere, while Dean is extremely practical and afraid of getting into trouble. Dean is always reluctant when Slim has a new idea, but Slim always wins him over and gets him to participate in the latest mystery.

Slim and Dean are sometimes helped by their friend, Arlen Bailey, who is extremely smart but capable of looking completely stupid while extracting information from others. The boys frequently have trouble convincing adults about the plots they suspect, so the boys are forced to work on the cases by themselves without adult help. The adults, especially Sheriff's Deputy Kingsman, act as frequent foils to the boys' plans.