Bitter Orange by Claire Fuller

Frances is hired to write a report on the follies in the garden of an old dillapidated home in England. There she meets Cara and Peter, a glamorous, hedonistic couple who dazzle Frances offering her their unexpected friendship. As Frances becomes increasingly entangled in their lives she finds that their stories don’t always quite add up. The lines between right and wrong, truth and falsehood become blurred and when a terrible crime occurs Frances is faced with the consequences of her blind love for people she barely knows.