© ITV/Mark Bourdillon

Teenage vandals smash a stained glass window at Midsomer Priory but the Prioress Mother Julian doesn’t want the police involved. But when Mother Thomas Aquinas is strangled to death, Barnaby and Jones must enter their cloistered world.


The Order of St Mathilde was celebrating its first new recruit for 30 years, but the murder leaves just three nuns. As well as Mother Julian and wheelchair-bound Mother Jerome, there’s Sister Catherine, a novice in her 20s.


In Midsomer Malham, Father Behan, chaplain to the Priory, complains to Barnaby that the nuns are reluctant to modernise, even though they have no money. Barnaby discovers the Order has a 200 year-old deed of trust, made by landowner Sir Anthony Vertue, which allows them to stay at the Priory for as long as a community exists.


Jones visits The Vertue Arms run by landlord Barry. Katy the barmaid reveals she saw a woman in old-fashioned clothes acting strangely on the day of the murder. Jones also learns that teenage couples sneak into the Priory grounds for romantic liaisons.


The nuns are shocked to find that their 17th century French silver altar set worth £60,000 has vanished from the safe. Mother Thomas wanted to sell the silver to help their finances. Did a dodgy dealer kill her?


Rich kid Duncan Hendred admits having sex in the convent grounds. He tells police that his trousers containing his new driving licence were stolen by a nun, but he denies stealing the silver. The Hendred family home is opulent, owned by his father Matthew. Hendred’s wife Lauren and Father Behan both seem nervous about the police investigation.


Sister Catherine is visited by her mother and step-father as she prepares to take her final vows. Barnaby learns Catherine’s late father was a descendent of Sir Anthony Vertue. If the Priory closes, Catherine would inherit it all anyway.


Lauren finds Father Behan dead, apparently strangled by Mother Thomas’ killer. At the Hendreds’ home, Barnaby and Jones find 100g of cannabis in Duncan’s room, but Lauren helps her son run away. Meanwhile, the missing silver is traced to an antique dealer in Oxford but it wasn’t stolen – Mother Thomas sold it on the day she died.


Barnaby realises Hendred’s years overseas hold a clue to the killings – he was a mercenary at the same time as Mother Julian was working as a missionary. Could an event from 30 years ago be the reason a nun and priest were killed? And is the killer about to strike again?