the Daleks using the bombs, but they are ineffective. David (Peter Fraser) rescues the Doctor with Susan while Barbara gets separated. Ian hides as the saucer leaves for the Dalek mining operations. There, he escapes the Slyther (Nick Evans), a pet of the Black Dalek. He eventually hides in the mine and becomes trapped in a capsule filled with explosives. The Doctor, Susan, and David arrive at the cliffs overlooking the mine; the Doctor sends David and Susan to interfere with the Daleks' radio signals, while he climbs into the mine. Dortmun sacrifices himself so that Barbara and Jenny (Ann Davies) can escape. They repair an old truck and head for the mining operations, but are reported to the Daleks when seeking shelter and sent to work. They are later brought before the Black Dalek and discover that the Daleks are drilling through the Earth's crust to blow out its core, the intention being to replace the core with a device to pilot the planet like a spacecraft. The Daleks imprison Barbara and Jenny and set the explosive-filled capsule in position, but Ian jams the capsule half-way down the shaft. The Doctor frees Barbara and Jenny. With the radio signals damaged, Barbara and the Doctor order the Robomen to destroy the Daleks, and the human slaves rebel. The bomb destroys the Dalek fleet and causes a volcanic eruption in England. Back in London, David begs Susan to stay and marry him. Susan agonises, declaring her love but admitting that she must leave. The Doctor locks the TARDIS doors and bids Susan an emotional farewell, telling her that she deserves a normal life with David. He promises to return one day, and sets the TARDIS in motion. Susan drops her TARDIS key and leaves with David. Production Conception and writing In March 1964, story editor David Whitaker formally commissioned Terry Nation to write a serial for Doctor Whos second season following the success of the Daleks from the titular serial of the first season, as well as Nation's quick and effective work on The Keys of Marinus. The commission was made under the title Doctor Who and the Daleks. Nation delivered the storyline for the serial in mid-April 1964 under the name The Return of the Daleks. The serial was retitled The Dalek Invasion of Earth by September; The Daleks in Europe appeared on some design material. The Dalek models were