The Solo Investigator's Handbook (2019)

Publisher's blurb:

The Solo Investigator's Handbook, a 95-page supplement for Call of Cthulhu. This product is the result of months of work and extensive playtesting, and contains a full system for generating on-the-fly, immersive adventures for your investigator(s). Using paper, pen, dice, this system, and your fevered imagination, you can generate full scenarios for yourself without the need for a Keeper. This is great if you cannot find a group, or for creating little scenarios for yourself in between your regular group games.