The Sibling Brothers

 by Jenkins W. Jenkins, is a series of mystery novels. The book that Dipper reads as part of his summer reading list is The Case of the Caper-Case Caper.

History
The book is part of Dipper's summer reading list. And while he enjoys reading the book, his out-loud reactions disturb Mabel when she tries to sleep at night.

Trivia

 * The Sibling Brothers is a parody of the "Hardy Boys" mystery series.