Cassandra is an Oxford don; Julia, her sister, a bestselling novelist. They share a set of disturbing memories of a strange childhood game and of Simon, the handsome young neighbour who loved them both.

Years later Simon re-enters their lives via a television programme on snakes and intrudes into their uneasy compromise of mutual antagonism and distrust. The old, wild emotions surge back, demanding and urgent, and this time the game is played out to a fatal finish.