Edward Stratemeyer 
Mystery at Putnam Hall [PDF ebook] 
Or, The School Chums’ Strange Discovery

An offshoot of Edward Stratemeyer’s abidingly popular Rover Boys series, The Mystery of Putnam Hall focuses on friends of the famous trio of brothers. When a shady character begins to hang around the venerable military boarding school Putnam Hall, a group of intrepid young detectives works together to put a stop to the strange goings-on before it’s too late.