Intriguing but ultimately disappointing because whoever wrote this didn't know how it should end. It was no cleverer than - let's make it someone no one suspects & have a spectacular ending.
But so many flaws. e.g where did knowledge of his caravan come from? What were the connections to previous foster parents? etc ...
& Why were the special effects of the fire in the house so amateurish?
Very disappointing that the writer wasn't able to draw the threads together.