The Riddle of the Third Mile is the sixth novel in Colin Dexter's Oxford-set detective series. As portrayed by John Thaw in ITV's Inspector Morse.

The thought suddenly occurred to Morse that this would be a marvellous time to murder a few of the doddery old bachelor dons. No wives to worry about their whereabouts; no landladies to whine about the unpaid rents. In fact, nobody would miss most of them at all. . .

Dr Browne-Smith passed through the porter's lodge at approximately 8.15 a.m. on the morning of Friday, 11th July. And nobody has heard from him since. By the 16th of July the Master of Lonsdale is concerned, but not yet worried. Plenty of time to disappear, think Chief Inspector Morse. And plenty of time, too, for someone to commit murder . . .

As bodies begin to pile, Morse sets out on a journey through intricate and complicated history, from World War Two Egypt to present-day London, in search of answers.

The Riddle of the Third Mile is followed by the seventh Inspector Morse book, The Secret of Annexe 3.