Anthony Gilbert 
Man in Button Boots [EPUB ebook] 

The most glamorous hotel in Europe is not immune to murder… Classic crime from one of the greats of the Detection Club When Julian Marks, a well-known diamond merchant, is found murdered at the Hotel Fantastique in Monte Carlo, the motive is presumed to be theft. Marks always carried with him an enormous diamond on a steel chain.Guests have noticed a shady character in button boots staying at the hotel. But when the diamond is found in an unexpected place, French sleuth M Dupuy has to rethink his investigation. Could the mystery man now lead him to the culprit?