Excerpt from the victim's diary.

25th December

I'm completely confused, terrified and desperate not to die. My parents are dead and my sister's fully insane. One moment she'll be cackling madly, singing to herself and the next she'll be lucid, staring at their corpses with tears in her eyes.

I'll run. Run away as far as I can before her next crazy episode. Maybe I can find the police and tell them what's happened before Jingle catches up with me.

Hopefully there's enough of my sister left in her to let me survive the night.