So this is set in the graveyard in Death In Heaven and I don't own Doctor Who. It should pretty much follow the same plot but it's been a while since I watched the episode.
The Mistress watches the Doctor's pet press herself desperately against the cyberman who was her boyfriend. It's really quite funny the way she insulted him before but now she seems to be trying to bring him back to life by crushing herself into the cold metal shell holding what's left of him.
Probably thinks she can revive him through the power of love or some such bollocks.
Humans- she never is sure why the Doctor is so fascinated by them.
His eyes catch hers, intensely cold and full of anger and rage.
It only makes her grin wider.
She swings her arms, pacing in front of him.
"Now- I'm not calling you a liar-" She declares, staring back with heated madness in her own eyes, "but that's because you know not to lie to me." The human girl is moving now. She tracks her from the corner of her eye. The Mistress truly finds it endearing how persistent the human race are. Like cockroaches really.
She gives him his present and- as expected- he refuses it.
Also as expected he gave it to the tin man to deal with. Always running. The Doctor through and through.
But oh, Clara. His Clara, her Clara, Clara Oswald, The Impossible Girl. Oh he wouldn't let her hands be sullied by the Mistress' weapon.
So he stares at her, horrified and playing for time and praying for someone to save him from killing her. The Mistress sighs theatrically.
"I'm going to let you kill me- you aren't ever going to get an easier shot than this." The Doctor still watches her and Missy is sure that if his pet was in front of him then even she would see, plain as day, the pain running through every crease in this new face.
He declares his intentions again, with a grim expression and his pet goads him on, trying to make him see what a monster she is.
Of course that would never work with her Doctor- he's always known. It's a shame his human pet doesn't realise. The Mistress would love to see those puppy dog eyes fill with disgust as her idol came crashing down.
"Rule number one:" She states loudly, "The Doctor lies." She catches one last glimpse of the hatred in the pet's eyes before she lands with a thump and an exhilarated screech.
She sighs, looking at the device around her wrist.
"I wish I didn't have to get a new one every time I do that..."