A Crack in the Line (Withern Rise Trilogy (Prebound))

When his mother died in a terrible train crash, Alaric Underwood's life began to unravel. Two years on and now sixteen, Alaric still isn't over the loss, and on the anniversary of the tragedy he stumbles into an alternative version of his reality. In this reality his place has been taken by a girl called Naia. Ages 12+.