While on the rock farm, the three Pie sisters Marble, Maud, and Limestone accidentally cause an avalanche, resulting in Holder's Boulder rolling and crushing both Igneous Rock and Cloudy Quartz Pie. Unsure what to do, the three sisters set out a train-ride across Equestria to gather all living members of the Pie family, expose old family secrets, decide how to break the news to Pinkie Pie ahead of her annual visit, and most of all, learn how to handle the guilt of their parents' deaths.