Pickering & Inglis Ltd., London, 1956; edition not stated but believe to be a reprint as worldcat.org lists first as 1954 and rear panel lists 13 titles in the ‘Sapphire Series’ with this listed as number 6.  Hard cover, 94 pages.  Red boards with black lettering on spine, black frame with two laughing boys’ heads on front.  Boards show light edge wear, corners and spine ends bumped and show light wear; binding sound.  Dust jacket with price intact shows edge and cover wear, some tears and edge tears, small losses at spine ends and corner folds, some scratches and creasing.  Interior clean and unmarked with tanning pages; two straightened corner bends; bright colour frontis (similar to jacket front panel); small spot on top page block.  “Douglas and Jerry, the principal characters, are fond of practical jokes and enjoy playing them on the masters at school.  The day comes, however, that the pair realise as followers of Jesus Christ they have to think twice before they get into unnecessary mischief.  Things begin disappearing at school and a detective is engaged to find the culprit.  After the mystery is solved, Douglas, Jerry and their friends form themselves into a society called ‘Junior Detectives Limited’ and are the means of unmasking an illicit gang and, incidentally, re-uniting Jerry with his father.” (from front flap)