In one of his last semi-lucid moments, John Gerrard swims around in small circles in a lake in Sweden, singing softly as the dusk descends. It is a haunting moment for his daughter and companion Nicci on this his last holiday. It is also prescient. As dementia claims his mind completely, the singing will cease and only solitude and darkness will remain. What Dementia Teaches Us About Love (Allen Lane, £16.99; Tablet price £15.29) is a powerful, poetic description of a daughter’s attempt to make sense of a much-loved parent who, long before he died, had “gone” but “remained” at the same time.