Cordelia lives with her twin sister Caroline in their central London basement flat. Years earlier, Cordelia had been caught up in a traumatic event that left her guilt-ridden and fragile. Her gradual recovery and search for independence is jeopardised when her sister leaves for a weekend away. For the first time she meets her mysterious neighbour Frank, a cellist whose music has intrigued her. As their relationship develops, Cordelia becomes convinced she is being stalked. Increasingly anxious and unsure of Frank’s motives, Cordelia begins to unravel.