Existance

When they met, The Doctor promised to keep her safe until she could go home.

But when they end up in a huge argument, The Doctor sends her away intending for only an hour or two.

But when it grew dark and she still hadn't returned, The Doctor goes looking for her, but what he finds, isn't what he expected.

Because of what she knew, he promised to protect her.

But,

Because of what she knew, someone wanted her dead.