Rollercoasters: Unique: Alison Allen-Gray (Tapa blanda)

When Dominic finds the photo in his granddad's loft, at first he can't believe what he is seeing. How can it be possible? How can there be someone else looking so like him? And then it beings to dawn on him that this must be his brother. But why has he never been told that he had a brother? Why has it been kept secret? And what happened to him?