The Forgetting. What isn't written, isn't remembered. Even your crimes. Nadia lives in the city of Canaan, where life is safe and structured, hemmed in by white stone walls and no memory of what came before. But every twelve years the city descends into the bloody chaos of the Forgetting, a day of no remorse, when each person's memories -- of parents, children, love, life, and self -- are lost. Unless they have been written.
Enemy, The (The Enemy Book 1) by Charlie Higson, http://smile.amazon.com/dp/B003SHDQD0/ref=cm_sw_r_pi_dp_x_NMuEzbT7YHKWV