Cully's boyfriend, Nico (Ed Waters), has temporarily moved in with the Barnabys, and is shadowing Sgt Troy to prepare for his new role in a TV show. He goes with Barnaby to Aspern Tallow Museum, where a 17th-century painting of Royalist and supposed spectre Jonathan Lowrie has been slashed. It looks like a case of nothing much until Barnaby finds a package of smoked mackerel on the grounds, bells toll in the middle of the night, Jonathan's descendant Marcus Lowrie (Charles Simon) is killed and sinister doings are afoot.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.