Original: The episode depicts a Dalek invasion of Earth led by Caan, Davros, and a red Supreme Dalek, who has kept Caan and Davros imprisoned in a section of the Dalek flagship, the Crucible, called "The Vault".
Simplified: The new Dalek army was led by a Supreme Dalek, who kept Davros imprisoned in a "Vault"; Davros said that he and the Supreme Dalek had reached "an arrangement".