Akatsuki boss Pein plants Kichirou Ren as a spy in the ANBU black ops squad. Simultaneously the ANBU black ops squad assign Uchiha Itachi to go undercover and infiltrate the Akatsuki. When both sides realise the situation, each man attempts to discover the other's true identity before it's too late. Sakura x OC, Sakura x Itachi. Spoilers.