Amy and Rory begin to wonder whether they should choose between normal life and “Doctor Life”. Many black cubes appear around the world and the Doctor stays with the Ponds to investigate but the cubes are inactive and the Doctor leaves UNIT, headed by Kate Stewart (Jemma Redgrave) in charge. A year goes by and the cubes suddenly begin activating random features before stopping the hearts of one third of humanity. The Doctor eventually tracks the cubes to the Shakri, who plan to eliminate humanity before they can colonise in space, believing them to be an infestation. The Doctor reverses the electric pulse used to stop people’s hearts and destroys the Shakri ship. At Brian’s urging the Doctor takes Amy and Rory back as full-time companions.