Blue Moon Princess

Am I, an English princess from the past???

You are a nurse living with your grandfather. On the night of a blue moon on your way home from work, a group of strangers wearing strange costumes attack you. You try to run away, and fall into a lake.

When you open your eyes, you find yourself in an unfamiliar place. For some reason, your grandfather is here too, and he calls one of the strangers “The prince”. They begin to explain your situation.