Thirteen Candles by Mary Hooper
It's Julia's 13th birthday, but despite all the celebrations, she can't get rid of the strange shivery tingle going down her spine. And why did the candles on her birthday cake blow themselves out on their own? Then, when she watches a home video of her celebrations, she notices a dark hazy shape leaning over her shoulder. She's sure it blew out the candles - but what is it?