On a perfect summer's day, at a school picnic beside a lake, four-year-old Gemma Anderson goes missing, leaving a family devastated and a community asking questions. Seventeen years later, Gemma's older sister Stephanie is practising as a psychiatrist. A new patient's revelations force her to re-examine the disappearance. Why are their stories so similar? Unable to let the matter rest, Stephanie embarks on a journey to find out what really happened to Gemma on that long-ago afternoon . . .