© ITV/Mark Bourdillon

A man is struck dead by a blow to the head as darkness covers Midsomer Stanton during a total eclipse of the sun. Jeremy Harper was a leading light in the village - an amateur astronomer who was passionate about preserving Moonstone Ridge, a Bronze Age heritage site which houses a 1930s observatory.


Barnaby and Jones discover that plumber and extra-terrestrial obsessive Peter Groves saw Jeremy argue with Lawrence Janson, director of the University observatory, before the eclipse. Local mystic Mags Dormer believes Moonstone Ridge is cursed - the sister of Jeremy's widow Catrina was found dead there years ago.


Jeremy was working on a secret project with an unlikely group of villagers - academic prodigy and PhD student Gagan Dutta, Peter and Mags' unemployed husband George. Meanwhile, Gagan's tutor Dr Adrian Sharp reveals the murder weapon was a meteorite.


Lawrence plans to close the old astrodome and build a new site on Moonstone Ridge. An angry Jeremy had threatened to campaign against his plans, which could jeopardise the Observatory's funding by solar energy company Panelsun International.


Mags pens a piece in the paper, claiming she predicted the murder, based on a reading with Catrina. Gagan's father Harry, a chemist and yogi who was married to Catrina's sister Mary, fears the astronomers are closing ranks, as they did when his wife died.


Harry tells Catrina he loves her but she confesses to an affair with Lawrence. Later, a spear-head and ancient sundial known as the Moonstone Disc are stolen from the heritage site. Red fibres from the scene match those on the rock which killed Jeremy.


Lawrence rubbishes Gagan's thesis, which in turn dismisses his published scientific work, and he's angry when journalist Tanya Walker quizzes him about the funding crisis. Then Peter is killed when the stolen spear-head is thrown like a javelin into his heart. A nervous George tells Barnaby that he suspects Harry. George is next to be killed, his throat his slashed by a throw from the Moonstone Disc.


Gagan calls for help, terrified she will be next to die. She, Jeremy, Peter and George believed they had discovered a new planet using stolen university data - and now all the others are dead. She's convinced Lawrence is the culprit. Meanwhile Harry is shocked to see her kissing Adrian.


Barnaby realises that the killer has been leaving a sign - the constellation of Scorpio. Both Mags and Lawrence are Scorpios. Barnaby knows Mags is hiding something but when Jones discovers Lawrence is also a decathlete - an expert at shot-put, javelin and discus - he's convinced he's found his man. But then Gagan goes missing...