Focusing on the famous cosmonaut Sirius Amory (pronounced SY-rus A-mer-EE), the story describes Amory's scientific investigation of "the Keywork", which, up until this point, has only been identified as a mysterious energy source that supplies nutrients to the 78 planets that make up Heaven's Fence. This expedition is overwhelmingly discouraged by Amory's wife, Meri, who considers it to be nothing short of suicide. Despite Meri's disapproval, Sirius goes forward with his mission. As the sole passenger on his spacecraft, the Meriwell, Amory's only companion is a computer system known as the All Mother, which also operates inside his spacesuit. The All Mother is tasked with analyzing and reporting Sirius' vital conditions throughout his mission as well as recording his findings. In order to obtain samples of the Keywork, Sirius leaves his ship and enters the energy source, his suit and the All Mother being the only things preventing him from instantaneous death. Quickly, Amory identifies the true source of the Keywork's energy as being the souls of those that have died. The souls maintain the characteristics and personalities of their previous lives and have the ability to infuse themselves with Amory. The first entity to come into contact with Sirius is Domino the Destitute. As the entity takes control of the cosmonaut, Amory relives the life of Domino.