Overview:It's the moment of truth for the final 12 as they perform live in front of the nation... with the first of two live shows as the final 12 sing live - and the judges each mentor one category of singers. Simon Cowell has the over 25s, Cheryl Cole has the boys, Dannii Minogue has the girls and Louis Walsh has the groups. Host Dermot O'Leary will be on hand to deal with the war of words as the judges give their views on each performance and defend their acts - one of which will leave the competition.