her Adam Dalgliesh series is absolutely my jam. If you want to read them in order, start with 'Cover Her Face' from 1962, then 'A Mind to Murder' (1963), 'Unnatural Causes' (1967), 'Shroud for a Nightingale' (1971), 'The Black Tower' (1975), 'Death of an Expert Witness' (1977), 'A Taste for Death' (1986), 'Devices and Desires' (1989), 'Original Sin' (1994), 'A Certain Justice' (1997), 'Death in Holy Orders' (2001), 'The Murder Room' (2003), 'The Lighthouse' (2005), and finally 'The Private Patient' (2008).
Her standalone novels like 'Innocent Blood' and 'The Children of Men' are great too, but they don't follow the same timeline as the Dalgliesh books. Her writing style is so crisp and the mysteries are layered—definitely worth reading in order to see how Dalgliesh evolves.