Grey Arthur is a very normal ghost. Too normal for his own liking. He's so normal he doesn't even know what group he belongs to: not scary enough to be a Screamer, or naughty enough to be a Poltergeist ... each different thing Arthur tries to be, he fails.
One afternoon, when Grey Arthur is thinking very despondantly how unfair life is, he senses the exact same emotion coming from a boy far away. And as he follows his instincts he reaches Tom's house.
Tom is a very normal boy, with brown hair and brown eyes and normal parents. But somehow people at school don't seem to think that. He doesn't fit in. People call him weird.
When Grey Arthur senses Tom's unhappiness he realises they're not so different after all. He doesn't feel he fits in with the other ghosts, either; and that is when he realises what he is going to be. He's going to be Tom's official Invisible Friend and help him solve his problems.