Degüello

Mid-October 1969, and a librarian is gruesomely murdered in the halls of the Bodleian, one of the most respectable rooms in Oxford. Morse and Thursday have little to go on beyond a set of muddy boot prints and two possible suspects, each known to have disagreed with the dead man. It looks like a contained academic mystery, the kind the city specialises in.

Then a new high-rise tower block, plagued by persistent problems, collapses catastrophically, and DeBryn's examination of the dead reveals a surprise that blows the whole case open. The trail of corruption and conspiracy runs from the local council up to senior levels of law enforcement, and it connects two seemingly unrelated crimes. It confirms the source of the adulterated heroin that has caused so many deaths, and finally solves the case that has haunted the Cowley boys for the past year.

It ends the way this show's finales tend to: with violence that feels both shocking and inevitable. DI Box shoots DS Jago dead, and Jago seriously wounds Box in return. The Cowley team is reunited at Castle Gate, and Morse moves into a familiar home, which after everything counts as a happy ending.

Russell Lewis wrote it, Jamie Donoughue directed. Shaun Evans is DS Endeavour Morse, Roger Allam is DI Fred Thursday, Anton Lesser is Chief Superintendent Reginald Bright, and Carol Royle is Mrs Bright. Alexander Hanson plays Councillor Clive Burkitt, Faith Omole is Olive Reynolds, Zaris-Angel Hator is Sandra Reynolds, Laura Donoughue is Deborah Teagarden, Michael Jenn is Osbert Page, and Precious Mustapha is Lucy Paroo.

The building collapse is a spectacular piece of television, all the more shocking for how ordinary the tower looks before it goes. The episode is the payoff for a season of careful groundwork, and it delivers the reckoning the Cowley boys have been owed.

A contained mystery that blossoms into something sprawling and systemic, and the season lands on a quieter note than it began.