Barnaby and Troy are called in to investigate at the museum in Aspen Tallow when the painting of a local historical figure, Jonathan Lowrie, is slashed. When the museum's curator is subsequently assaulted and Lowrie's direct descendant is murdered, the detectives must unravel another mysterious knot. Barnaby does focus on one important clue, however: a packet of smoked mackerel inadvertently dropped in the cemetery. Meanwhile, they are joined by Nico, Cully's actor boyfriend, who has landed a part in a TV series as a detective sergeant.