It has to be said, a peculiar story! This is supposedly written for young adults, but it shouldn't be restricted to that audience.
The book is illustrated with bizarre old photographs the author has found in second hand shops and boot sales. They are 'trick' photos showing peculiar situations: a child standing by a pond, with two children reflected in the surface of the water. A small girl levitating...
The characters in the story are these children, who live on an island, in a home which accommodates all their peculiarities. A boy and his father arrive on the island to look into some family history and the boy stumbles across these children, and a portal through which he enters and discovers the secret his grandfather was trying to pass on to him.
Very engaging, worth reading. Quirky.