Pulled into the past to discover his future

Abandoned in a shopping mall when he was a baby, thirteen-year-old Tom Mullen has no family - he's spent his life shuffled from one rotten foster home to another. When he hears rumors that a mass grave has been unearthed on his school grounds, he feels himself inexplicably drawn to it, and then down into its terrible darkness and beyond. He discovers that he is no longer in Liverpool in 1974 but in Ireland in 1847, the height of the potato famine. A family named Monaghan takes him in, and Tom experiences for the first time what its like to have parents and siblings who cleave to one another even amid terrible hardship. But why has Tom been transported across time and place? And why must the grave keep yanking him back, at intervals, to his dreary, lonely existence in Liverpool? Most of all, what does it mean that the Monaghan's son Tully is practically Toms double? Tom stands by the Monaghan's in their plight, and in so doing discovers that the past, and the Monaghans, hold the key to his destiny.