Although Gravity Falls ended after just two seasons, The Book of Bill tie-in project reveals more about both the strange titular town and the mysterious Bill Cipher. Penned by Gravity Falls creator Alex Hirsch, who also voices Bill in the TV series, The Book of Bill also serves as a solid continuation of the Twin Peaks-inspired horror-comedy show. Well before Bill Cipher is formally introduced, the show follows twins Dipper (Jason Ritter) and Mabel Pines (Kristen Schaal), who arrive in the strange town of Gravity Falls to spend the summer with their great uncle, Grunkle Stan (Hirsch).

A grifter of sorts, Grunkle Stan runs a tourist trap called the Mystery Shack, which capitalizes on the Oregon town's string of supposedly paranormal happenings. While Stan is billed as a classic skeptic who's set on swindling people, Dipper wants to believe in the supernatural goings-on, especially after he finds a mysterious journal in the forest.