The Mystery of the Missing Necklace is a book in the series of Five Find-Outers and Dog by Enid Blyton, published in 1947 by Methuen and illustrated by Joseph Abbey.
Why is Mr Goon, rushing around Peterswood looking extremely busy? The Find-Outers want to know why, and so ask their very good friend, Inspector Jenks, in the next town. He informs them that Peterswood is the meeting place of a very clever gang of jewel thieves. So the Find-Outers decide to try and help the police, by keeping their eyes open for anyone who looks suspicious.
Fatty very cleverly disguises himself as an old man, sitting on a bench in the village so he can observe anything unusual without looking suspicious. Meanwhile, Mr Goon is also Conducting his own investigations when he finds out the meeting place of the Gangs, In the middle of the night Mr Goon and his men raid the meeting place where a meeting of the Gangs was ongoing The entire Gang was arrested but one man managed to escape taking the necklace with him.
The man was later arrested but the necklace was not found. Mr Goon and the children are now searching for the missing necklace before The last remaining person of the Gang (who was not in the meeting place) Finds the necklace. The Find – Outers Later Find the necklace and the last man of the Gang was arrested.