Arcadia

April 1967, spring blooming all over Oxford, and the artist Simon Hallward dies in a horrendous house fire that leaves the City Police baffled as to the cause. Not long after, a young housewife dies of what looks like a stomach bug, the same mysterious complaint that has put half of Chief Superintendent Bright's men on sick leave. Morse's instinct says the two are connected, and the instinct is right.

The trail leads to a cult-like commune Hallward had left months earlier, and then to Richardson's, a local supermarket owned by a wealthy family descended from a line of Quakers. The food on the shelves is tainted. The owners are being blackmailed and refuse to pay. The blackmail culminates in the kidnapping of the Richardsons' daughter, with a ransom demand that appears to come from a dead man.

Morse has to hold fire, illness, supermarket scandal and abduction in his head at once and find the single thread that ties them. The pieces are darker than anyone wants to admit, and the episode keeps the period flavour sharp while it goes about it.

Russell Lewis wrote it, Bryn Higgins directed. Chris Larkin is Ivor Maddox, Genevieve O'Reilly is Annette Richardson, Charles Babalola is Cuthbert Mukamba, and Shvorne Marks is Monica Hicks. Richard Dillane plays Leo Richardson, Joanna Roth is Prudence Maddox, Tom York is Mike Maddox, Roger Allam is DI Fred Thursday, Caroline O'Neill is Win Thursday, and Sara Vickers is Joan Thursday. WPC Shirley Trewlove joins the station along the way, and DS Peter Jakes takes his leave.

The commune, the supermarket and the Quaker lineage give the episode a lot of period flavour to play with, and it uses every bit of it. There is also a bittersweet undercurrent to the station business, with Trewlove arriving and Jakes leaving, the cast of the show quietly changing the way teams do.

A satisfyingly crowded piece of plotting, and one that knows exactly how to keep the mystery rising.