It is Don's turn to be in Fishmouth. There's the festival going on. Try to find some cultists that make sense.
Unlike normal walkthroughs, in Nice Game Hints you can select just the puzzle you want hints for. Here are listed the puzzles for "Fishmouth Festival" in Gibbous - A Cthulhu Adventure. The guide you choose only contains information about that puzzle, reducing possible spoilers for other puzzles.