Collecting his post in the London of 2012, the Doctor and Ace are called through time to south-east Scotland to help out an old friend — an old friend who’s vanished. They find themselves at Graystairs, an Alzheimer’s treatment clinic and a place of healing, where the patients seem to be gaining a new lease of life. But whose life is it? Soon, the Doctor and Ace find out the hard way that actions have consequences — and that there’s more than one kind of dementia.