Maggie Eliot, Appleton Fellow for Global Issues at Merrion College, Oxford, is having an eventful sabbatical year. She has overcome writer's block, fallen in love and gotten married. She is now enjoying summer with her husband Thomas, who is also the 28th Baron Raynham, at Beaumatin, his Cotswolds estate. Thomas takes Maggie to visit St Margaret's House, a residence for Benedictine nuns suffering from dementia and Alzheimer's disease. There she meets Meg, who volunteers at the residence. Meg gives Maggie a sealed envelope and asks her to keep it safe but not open it. Maggie reluctantly agrees to keep Meg's secret. Then Maggie finds Meg murdered in the St Margaret's chapel.

Another murder follows and the police think Maggie may know the man the media are calling the "Gloucestershire Garrotter." When Maggie at last opens Meg's mysterious envelope, what she finds inside could well explain the murders. And she can only hope that the killer's identity is discovered before she becomes his next victim.