It's a fiction, takes place in San 
Jose,
Costa Rica, around 40th or 50th. The main character is a guy who was 
sent to
San Jose to work in some American news paper. Then he goes to another 
town
to see the carnival with an acquaintance (another American) from San 
Jose
and his girlfriend, this girlfriend gets into some sort of trouble at 
the
carnival. I think they made a movie based on the book.

There is a film called "Carnival in Costa Rica." I haven't found any
evidence that it was based on a book.

"Carnival in Costa Rica (1947)
Fun musical set in Costa Rica stars Dick Haymes as a visiting American
who falls in love with local girl Vera-Ellen...who happens to already
be engaged to playboy Cesar Romero...who happens to really love
American Celeste Holm! Also starring J.Carroll Naish and Anne Revere."

http://www.cabbageboymovies.com/holm.html