The publication order is a factual answer, but the reading order could be thematic. If you want psychological depth: 'Folly', then 'Keeping Watch', then 'A Darker Place'. If you want historical atmosphere: 'Touchstone', then 'The Bones of Paris'. If you want a tight thriller: 'Lockdown'. But for the simple list of what was published when: 1999, 2001, 2003, 2007, 2013, 2017 with the corresponding titles. That's the answer to the question as asked. It's a compact list compared to her series output, which makes it manageable to collect and read over time. Each book is a substantial meal, not a snack.