Fire and Hemlock by Diana Wynne Jones

I don't know if I'm happy or annoyed with myself for not picking up this book earlier. I've had it for ages. It's bloody brilliant.
All the same, I'm over the middle right now and can't wait to find out how it all ends. The temptation to leaf to the end and have a quick peek is great. I'm resisting.

Nothing much really happens in this book. It takes place in GB in modern times. It's just a life of a girl, called Polly, from age 10 to 19. Only one day, at 19, she suddenly discovers that she's got another set of memories in her head - a set she'd completely forgotten and didn't know about. About people, things she'd done, strange things, too. And now, she's remembering.
And there's this person, Tom. He's a grownup, ordinary man, who she met when she was 10 at a funeral, of all places.
They took a liking to each other, and started playing a game - "Let's pretend you're not you". They invented that Polly would be assistant-hero in training, and Tom - a hero in training, and they'd tell each other stories how those two would kill dragons, fight wizards etc. Sometimes, when they are together, these stories almost come true, in a sort of and round-about way. Polly and Tom are not sure they want to believe it's not a coincidence.
And then there is the family of Tom's ex-wife. Seems right nasty people. And also seems they are somehow controlling Tom, and they don't like Tom's friendship with Polly. They hate it, actually. And they can do stuff to split them up and hurt them, strange stuff. Like making garbage flow together into a great, ugly shape-monster and pursue them. Or make Polly's mom hate her and put her out of home (that one ends well, Polly gets to live with her grandmother). Or bring to life tin-armour in an amusement fair's House of Horrors, and attack them. Yes. Well. As I said before, strange stuff.
And that's how far I've gotten. And I think they won't be talking anymore after this last incident - there were hints about it earlier. And Polly will forget everything - how? Why?
I want to find out all the answers. That's a DWJ's book, she usually gives out all the explanations in the very last chapter, along with a grand-finale scene where almost every character participates. That's her thing.
And I love her style in this book. It's very languid and unhurried, with ample amount of strangeness, action and tension. Her readers are kept guessing and waiting impatiently to get back to reading.