What is the vibrant and colourful event of carnival all about?

The Brazilian 2012 Carnival officially kicked off in Rio on Friday 17th February (festivities started the previous day in places like Salvador de Bahia), and will run for five days. Carnival provides one of the main turning points in my novel, Carnival of Hope, when Tomas and Thereza, the main characters, begin to discover that rather than offering hope of a job in a Southern city, the carnival competition is a life-threatening deception. So, what is this vibrant and colourful event all...