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Read Adam Sweeting's review of "Intelligent Design", the last-ever episode of Lewis

Although its steepling body count is almost enough to rival the trail of carnage in The Walking Dead (which rose from the grave on 5 last night after its original appearance on FX last year), at least Lewis never underestimates the value of a good education. This episode, "Wild Justice", was a crossword puzzle of literary clues, all taking their cue from a lecture delivered at St Gerard's college entitled "Justice and Redemption in Jacobean Revenge Drama".

There were recurring appearances by John Webster's The White Devil, and a nod to Shakespeare's Titus Andronicus, from where this week's murderer had borrowed the idea of a starved and partially buried corpse. The episode title was a quote from Francis Bacon. That only left the mystery of Fulworth's The Devil's Friar, cited as a source of death by suffocation, but a work so obscure that not even Google has heard of it.

No matter. It was all part of the sinister warp and macabre woof of the goings-on at St Gerard's, a strange institution bearing a semi-detached relationship to Oxford's other colleges. It had been privately funded for generations by the Goffe family, currently represented by Adele Goffe (played by an actress billed as Sîan Phillips, pictured below, who must have been on an epic cosmetic surgery binge), and was largely run by hooded friars.

As regular viewers will know, Lewis's irascible sidekick, DS Hathaway (Laurence Fox), trained for the priesthood before joining the rozzers, and it was he who gave us a capsule definition of friars: "Monks stay in and chant a lot, and friars get out and about."

One of them had been getting out and about with lethal vigour. The trail of dead which began with the death by poisoned chianti of visiting American bishop Helen Parsons (Pamela Nomvete) took on an ecumenical bent by encompassing a retired policeman (a rare sighting of Christopher Timothy, pictured below), another friar, and the son of a college professor. Multiple motives and sundry digressions ensured that picking the killer was impossible until a long and elaborate back story had been sprung on us. With hindsight, we could see that screenwriter Stephen Churchett had worked a little too hard to build up the significance of the college election in which a successor would be chosen for the current Vice Regent, Friar Mancini (Ronald Pickup).

But the pirouettes and curlicues of the plot are merely Lewis's window dressing, and it's the relationship between Lewis and Hathaway that makes the thing worth watching. In fact, it sometimes seems more interesting than the slightly ponderous master-and-servant routine Lewis used to go through with Morse, in which the latter's name-dropping of opera conductors or poets to his uncomprehending, footsore underling eventually became pointless.

The Hathaway-Lewis balance works because while Hathaway is an academic who judges fools harshly, Lewis is the boss and he knows he's good at his job even if he can't summarise Proust. Hathaway's mouth tightens irritably at the sight of a misplaced apostrophe, and he delivered an acidic put-down of Lewis's attempt at Italian pronunciation, yet his ascetic intellectualism fits neatly with Kevin Whately's blokeish, instinct-and-common-sense approach.

The pair of them also found common cause this week in their respective doubts about their careers. Lewis is beginning to hear the siren voices of advancing middle age, and encroaching grandfatherhood, telling him it's time to hang up his badge. Hathaway still isn't convinced he should ever have become a policeman at all, and is sorely tempted to go native when he finds himself rubbing shoulders with university professors. In an episode which ended with a laughably histrionic denouement, these were things you could believe in.

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