Start with A great deliverance, and read in publication order without deviation. The book exists to force the pairing — Thomas Lynley, an earl working as a detective inspector at New Scotland Yard, and Barbara Havers, a working-class sergeant who resents everything he represents, both being punished by the assignment. Almost every dynamic the next twenty years run on is set here.
The alternative that tempts people is A suitable vengeance, because it is chronologically a prequel: it takes place before the first three books and it explains Lynley's Cornwall estate, his mother, his brother and why a man with that title carries a warrant card. Read it fourth, where Elizabeth George published it. It answers questions the earlier novels have already made you ask, and reading it first removes the point of asking them.
What order actually means here
The cases are self-contained. The series is not. Lynley and Havers run strictly in publication order, the supporting cast arrives with a shared history that is doled out rather than explained, and Payment in blood opens on consequences from the first book. If what you want is a good English murder rather than a twenty-year relationship, read the first two and stop — that is the honest exit, because the payoff of everything after is cumulative.
The first two
A great deliverance and Payment in blood, about three weeks for 700 pages. These are long crime novels with far more interiority than plot: expect whole chapters inside a suspect's head, and expect the murder to be solved less by evidence than by somebody finally saying what they have been avoiding. Keep a page for the recurring cast — Lynley, Havers, Lady Helen Clyde, the forensic scientist Simon St James and his wife Deborah — and add a line whenever a piece of shared history is dropped in, because it is never re-explained.
The early cases
Well-Schooled in Murder, A suitable vengeance, For the sake of Elena, Missing Joseph. Seven or eight weeks for about 1,920 pages, and the most evenly paced stretch in the series. Well-Schooled in Murder is the first case where Lynley's class background is directly in the way of the investigation. For the sake of Elena hands an unusual amount of the book to Havers, and this is where her story stops being colour. Missing Joseph is noticeably the longest and slowest; give it a fortnight.
The middle stretch
Playing for the ashes, In the Presence of the Enemy (Inspector Lynley Mystery), In pursuit of the proper sinner — three books averaging over 670 pages, so plan 30 pages a day rather than 40. Playing for the ashes is the first real structural experiment, with half the book delivered as a young woman's confessional journal that contains the solution. In the Presence of the Enemy (Inspector Lynley Mystery) keeps Lynley off the page for long stretches. In pursuit of the proper sinner opens with a professional rupture between Lynley and Havers that drives several books after it.
One gap to know about: that rupture arises from events in Deception on His Mind, a Havers-centred novel published between those last two books and absent from our catalogue. You will not be lost without it, because the following book explains what happened, but the disciplinary trouble hanging over her did not come out of nowhere.
The turn
A traitor to memory is 864 pages and the longest in the series; it is slow by design and it is the book most readers abandon, almost always from pace rather than quality. Give it a fixed daily page count and stick to it. Then With No One As Witness, which is the hinge of the whole series — do not read the jacket copy, the reviews or the wiki entry first. What Came Before He Shot Her follows, is barely a Lynley novel at all, and tells the story behind the previous book from the other side. It is the most divisive volume here: some readers call it her best work and others resent 700 pages away from the detectives. It is not optional if you want the turn to mean what it is meant to mean.
Where to stop
This is where the path stops, not where the series does — George has continued well past this point. What ends here is the need for a map: after What Came Before He Shot Her the arc has been reset and you can simply carry on in publication order. If you want another long-running English detective while you decide, Inspector Rebus is the obvious neighbour.
Follow the full ordered path here: Inspector Lynley Reading Order: Where to Start.