Twin Peaks co-creator Mark Frost’s tie-in novel, The Secret History of Twin Peaks, had the conceit that it was an in-character mass of documents that FBI Agent Tamara Preston was looking over and annotating after their discovery at a crime scene, thus providing a wealth of new information about the history of the town from before its founding right up to the end of the original series, recontextualising material, rehabilitating some of the dross from the limp end of series two, and acting as a delicious appetiser for the weird banquet that was Season 3. Like I said in my review of the Secret History, it was basically a Twin Peaks take on House of Leaves.
If the Secret History was an appetiser, The Final Dossier is a last cup of coffee and an after-dinner mint. Substantially shorter than The Secret History, it takes a similar premise but has a much more straightforward presentation, being a coda to season 3 assembled once again by Tamara Preston, detailing her various discoveries about what’s been going on with the town and its residents since the end of series 2. However, rather than being a lovingly compiled set of deliciously fabricated documents with Tamara’s commentary, it simply provides Agent Preston’s direct summary of her findings. (The sole exception is an autopsy report on a major character from the original series who was conspicuous by his absence from season 3.)