E. Phillips Oppenheim 
The Spy Paramount 

The Spy Paramount takes us to Rome, 1934. American Martin Fawley, a former secret service agent, is recruited as a spy by General Berati, the most feared man in fascist Italy. Going undercover to Monte Carlo, Fawley travels in a world of casinos and cocktails, high stakes and secrecy—and discovers the secret weapon that could determine the outcome of the looming world war.

The heroe in this novel is a super-spy, freelancing in the interests of world peace… He is the strong, silent type who falls at last and therefore very heavily in love…