Mickey joins the Doctor, Rose, and Jack when they travel to Cardiff to refuel the TARDIS at the rift. Suspicious of her actions, they apprehend the Slitheen who is posing as Margaret Blaine after learning that she is now the mayor of Cardiff. In addition to having an extrapolator that she would use to escape, the Doctor discovers that she has built a nuclear power station that is intended to unleash the gap and destroy Earth. Since she is a criminal on her home planet and would face the death penalty there, Margaret refuses to being returned. Margaret asks to be transported to a different planet following multiple unsuccessful attempts to murder the Doctor. Jack thinks he can use Margaret’s extrapolator to expedite the TARDIS’s recharging process, but it turns out to be a trap because it was designed to deliver the closest alien power source to the rift. When Margaret looks into the TARDIS’s heart during an earthquake in Cardiff, she is given a second chance at life and is transformed back into an egg.