At a remote farmhouse the body of keen photographer Idris Williams is found. At first it seems that this is a case of a burglary that went horribly wrong, but Mathias' instincts tell him otherwise - this was murder.
Could his death be linked to a series of murky land deals made by his father, who disinherited a neighbour, Eric Roberts, years previously? What secrets do the mountains hold about the deaths of three German prisoners of war on Welsh soil in 1944? And what involvement does 'The Guild' - a local organisation of professional men - have in this historical jigsaw?