The Changeover
Margaret Mahy1984

A clammy hand pressed Laura down onto her knees beside Jacko's bed. It was the hand of terror, nothing less.'
It was a warning. Laura felt it when she looked in the mirror that morning. There had been others: the day her father left home, the day she met Sorensen - the boy with the strange silver eyes.
But nothing had prepared Laura for the horror of today. And now her little brother, Jacko, was fighting for his life after being sucked dry of his youth by the sinister Carmody Braque.
Laura knows there is only one way to save Jacko; she must join Sorensen and use his supernatural powers to change over if there is to be any hope for her little brother.

Titre original : The Changeover (1984)