Quantum Shade Quantum Shades were beings that could kill specific people regardless of their location in space and time . Their victims would be marked with a chronolock , a tattoo - like brand on their neck , counting down the minutes to their death . At some point , Me allied herself with a Quantum Shade that had taken the form of a raven , using it to enforce her law in an alien refugee camp ; the trap street in London , where she was mayor . Whoever broke the law would be marked with a chronolock , given enough time to say goodbye to their loved ones before their death . The mechanism of the chronolock allowed for it to be transferred only once to someone willing to take it on ; that person would then die in the place of the original condemned . Mayor Me had the authority to remove the chronolock from the original condemned , though usually chose not to in order to maintain rule of law , given the fact her camp included many warlike species ( including Cybermen and Sontaran s ) that would not respect her authority if she rescinded punishment . Me could not remove the chronolock from the new victim after it had been passed on . The Quantum Shade was physically connected to Me by way of a tattoo - like marking on her chest that would trigger the raven ' s attack on the condemned . The Quantum Shade rendered a quick , but painful death on a target . At one point , Me says the Shade is " promised a soul " but it ' s unclear whether this is literal . After Rigsy was lured into the camp and accused of murdering one of the refugees , he was marked for death by the Shade and Retcon ned prior to his release ( even though doing so rendered it impossible for him to say goodbye to his family ) . After discovering the tattoo and calling the Twelfth Doctor and Clara Oswald for help , the trio located the camp and investigated the crime in search of proof of Rigsy ' s innocence . When Clara learned that someone else could take the mark , she volunteered to take it from Rigsy , not wanting his daughter to grow up without a father and believing Me would save her since she had declared Clara to be under her protection . She managed to convince Rigsy to give her the chronolock . However , they soon discovered the " murder " was staged to be a trap for the Doctor and Clara . Me had made a deal with the Quantum Shade that she could remove the chronolock from Rigsy at any time . Attempting to do so , Me and the Doctor discovered that Clara had transferred the chronolock to herself . Me informed Clara that , in taking the chronolock , she had removed Me from any deal she had made with the Shade , rendering her unable to remove it as she normally could ( notably , when the raven was triggered , the markings sported by Me did not change ) . After saying goodbye to the Doctor , Clara was killed by the Shade as the horrified Doctor watched . ( TV : " Face the Raven " ) This event led the Doctor into a desperate , 4 . 5 - billion - year bid to somehow save her life . Returning to the moment before the raven entered her body , the Doctor withdrew Clara from the timestream , though ultimately he was only able to delay the inevitable . The chronolock marking remained on Clara ' s neck and although she had untold adventures on her own and travelling with Me , eventually the laws of time demanded that she return to the moment of her death , allowing the Quantum Shade ' s contract to reach its conclusion . ( TV : " Heaven Sent " / " Hell Bent " ) Behind the scenes . Sarah Dollard , writer of " Face the Raven " , has said on her Twitter that once the Chronolock is transferred to another person and Ashildr is cut from the deal , the Quantum Shade can ' t be stopped by anyone .