Special Investigation Bureau (SIB) is the elite plain-clothes detective unit of the Royal Military Police and investigates serious crimes connected to members of the British Army. Sergeant Jo McDanagh, played by Tamzin Outhwaite, was recently posted to SIB from Close Protection. The SIB is a man's world, as Jo has discovered. Having proven her detective skills, if not her diplomacy, she is now a full member of the SIB. She must still watch her back though - SIB gives no second chances any more than it accepts mistakes and the cases to which she is assigned are not getting any easier.