W.E. Johns 
Gimlet Gets the Answer [EPUB ebook] 

The story starts with Major Charles of the Intelligence Office briefing Gimlet, Cub, Copper and Trapper about a gangster called Nicolou “Knifey” Kniftos. Knifey had been forced to leave America when he fell foul of other gangsters and settled on Cyprus. Here his behaviour has been suspicious and now he has been back to America and is returning to Cyprus in a private yacht called the ‘Sandra’, with six other well known gangsters. Major Charles wants to send Gimlet to Cyprus to find out what he’s up to.