A phrase referenced in the thoughts of an injured Skum in Chapter 46 as something that was supposed to start.
Ray contemplated the phrase in Chapter 47 and thought of it as not necessarily language from Hastur’s holy texts, but something about the idea of collecting and bringing things home reminded Ray of Hastur’s dogma–perhaps created by creatures within their own milieu.
In Chapter 50 (Part 2), a platoon of Skum attacked the Sellen Starling, seemingly as part of what they believed to be the Great Harvest.
In Chapter 51, shortly after midnight on 6 Neth, the party witnessed what they believed to be an aborted attempt to enact the “Great Harvest.” A blazing column of light blasted out of Iris Hill and into the night sky. Then another erupted from the star stela atop Gladiolus Hill, where humanoid shapes were seen to be gathered. The air in Thrushmoor lit up and wavered, vibrating in pockets where reality seems to oscillate between two locations—the Thrushmoor of Golarion, and a Thrushmoor of Carcosa, and in the Thrushmoor of Carcosa, Iris Hill was replaced by a windowless tower with battlements. However, the stela on Crocus Hill failed to complete the triangle—because the heroes aboard the Sellen Starling prevented the Skum from being there with their victims.
First Reference: Chapter 46
Other Notable References: Chapter 47, Chapter 50 (Part 2), Chapter 51