A fatal inversion - Barbara Vine

In the long hot summer of 1976, a group of young people are camping in Wyvis Hall. Adam, Rufus, Shiva, Vivien and Zosie hardly ask why they are there or how they are to live; they scavenge, steal and sell the family heirlooms. In short, they exist. Ten years later, the bodies of a woman and child are discovered in the Hall's animal cemetery. Which woman? Whose child?
'I defy anyone to guess the conclusion ... the clues are cunningly planted, so that it seems one should have known all along. A most satisfying end' Daily Telegraph