Barney sits in a chair and recalls the day he was hit by a car. His back was broken and his wife was killed. Although he can now walk, the pain of the memory is not so easily healed. But what is memory? This film takes a remarkable journey through our minds - from how memories form to why they unravel in old age. We think of ourselves as inhabiting our bodies, but are our most precious recollections little more than an arrangement of cells in our brains? And as scientists understand more about how memories are formed, could difficult memories be adapted and changed so they are less painful?