The Frank and Joe Hardy: Detective Brothers series was aimed at younger readers, students in third and fourth grades. It was published from 1997 to 2000 and was discontinued due to low popularity. This series is significantly different from other Hardy Brothers books. So, the Hardy Brothers do not deal with serious crimes in it. In these books, Frank and Joe are only 9 and 8 years old, respectively, and attend Bayport Elementary School. Frank Hardy is nine and Joe is eight and has just moved to Bayport. In search of a missing baseball glove, the brothers climb into a creepy old house, and find a skeleton, brain and blood - this is where the real mystery lies. Source: