Jennings follows a clue - Anthony Buckeridge

Fossilized fish-hooks! 'We must have a headquarters, where we can meet and work out clues and things.
We might even put up a notice so that chaps will know where to come when they want mysteries solved. Something like Linbury Court Detective Agency - Chief Investigator, J C T Jennings?' When Jennings is inspired to take up a career as a detective, with faithful Darbishire as his assistant, trouble is bound to be just around the corner. Their first mission - to recover a 'stolen' sports cup, is the first of several bungled attempts to imitate super sleuth Sherlock Holmes. Frightful bish! But the detective duo face their most perilous adventure yet when they make a nocturnal visit to the sanatorium and discover that they are not alone. An intruder is at large, but a missing coat button is Jennings' only clue. Crystallised cheesecakes!