Doomsday follows the daily lives of the residents of Yesterday's Promise: a millennial cult and self-sustaining green-community hidden in the Catskill mountains. Featuring both present action inching toward doomsday and flashbacks revealing how and why each member came to join the secretive sect, the series explores the gray area where youthful idealism evolves into deadly extremism and documents the eerie final months leading up to a horrific Jim Jones style massacre.