The campaign begins in the year 1890 and follows the investigations of the Merriweather Society for the Investigation into the Paranormal and the Supernatural.

Each player controls a couple of investigators (although only actively plays one investigator per investigation) that are members of the aforementioned society.

Typically there are a couple of investigations per year, with the downtime being spent in training and learning about the Cthulhu Mythos as well as going about their normal lives, though nothing could ever be normal again after encounters with the Cthulhu Mythos.