the mastermind [tua]

In which a lethal prodigy finds something worth living for in the midst of an apocalypse and a cold hearted time traveller learns that there is still good in the world he is so desperately trying to save.

OR

In which Maeve Kenning is exiled from the Commission and wants to live a usual and quiet life in the 60s, until her arch nemesis finds her and convinces her to try saving the world.