Secret Seven Mystery by Enid Blyton

A puzzling incident close to home sends the club on a trail of odd clues, suspicious comings and goings, and a shadowy figure lurking nearby. Through secret meetings, careful observation, and the help of their loyal dog, they untangle the riddle and set a trap to catch the culprit. In the end, their teamwork restores order and proves that sharp eyes and steady courage can crack even a thorny mystery.