The Department of Temporal Investigations Reading List is centered around the series of novels following the adventures of Marion Dulmur and Gariff Lucsly, agents of the DTI.
In addition to the main novel line, several other novels and short stories which feature Dulmur and Lucsly are connected due to various references in other books, or to other books. These references are mentioned in the notes. Various references in parts of the anthology New Worlds, New Civilizations connect the Dulmur and Lucsly story from that work.
Dark blue denotes the primary novel narrative. Read these for the bare bones story. Light blue denotes the expanded storyline. Read any or all of these to go a bit deeper. The white denotes every other connected story, regardless of overall continuity.
Hover for notes. As always, not every reference to every other story is mentioned, just the one I chose as most important to show the expanding Lit-verse web.