Who is Tom Ditto?

'Dear Tom, I have not left you, but I am gone' ... Has Hayley gone or hasn't she? What is Tom supposed to do in the mean time? Trying to work out what's happening to his confused life, Tom tries to track Hayley down. In doing so, he stumbles across a strange group of people with a highly-addictive hobby. Next, he's being followed ... Who is Hayley? Who is this new girl following him around the supermarket? And who, for that matter, is Tom Ditto?