It is 1906 and the Faro family gather in Orkney after the untimely death of Faro's son-in-law Erland Yesnaby. As they rally round the grieving widow Emily, their attention is caught by strange activity aboard the royal yacht anchored nearby instead of the main harbour. When a passenger's body is washed ashore, neither Faro nor his daughter Rose McQuinn can resist the mystery unravelling on the island coastline.
As they delve deeper into the case, Lammastide breathes sinister life into the ancient selkie legend with unexplained accidents and brutal attacks on two young men. When shocking truths are uncovered about loyal and trusted servants, Faro and Rose quickly realise the lives of more than one member of their family might be in danger – and time is running out for them.