The androids produced by the Kraals were utilised by Styggron as part of his plan to colonise the Earth. Through the use of a pattern analyser the memories and intelligence of the subject, as well as there appearance, were transferred to an android.
Styggron had a replica of the village of Devesham and the nearby Space Defence Station created on the Kraal homeworld of Oseidon to function as a training ground for the androids. This continued for an extended period, despite Marshal Chedaki's criticism, as Styggron hoped to use the androids for further invasions after Earth was taken, so the techniques needed to be extensively tested.
Guy Crayford, who had no duplicate, served Styggron as leader of androids based in the Defence Station. The village was populated with androids, matching the inhabitants of the real one. Other androids, service mechanics, which wore white overalls and helmets with dark-tinted visors, patrolled the area. They were armed with weaponry fired from the index fingers of their right hands. Styggron produced a duplicate of a UNIT soldier programmed to become hostile to Kraals, against which he demonstrated the effectiveness of the weaponry he had developed, destroying it.
The Fourth Doctor and Sarah Jane Smith found themselves in the Devesham replica while attempting to get to Earth. They found inconsistencies in the reproduction, such as coins that were all minted in the same year, phones that didn't work and a dartboard that had never been used. When Sarah attempted to converse with the locals in the Fleur-de-Lys, she was told by the android Adams that they didn't have strangers there.
Sarah was captured by Styggron who produced an android replica of her. The Doctor quickly noticed the switch though as the real Sarah had lost her scarf while the android wore one. She displayed other uncharacteristic traits too, such as a taste for ginger beer, where her human counterpart "[couldn't] stand the stuff".
The real Sarah destroyed her android captor by using electricity with water as a conductor. An android duplicate of Harry Sullivan helped Styggron prepare the virus he intended to wipe out humanity with, unable to touch it himself due to the risk of contagion.
The Kraals intended to use the androids to release the virus on Earth. Some were loaded into retro tubes, including a duplicate of the Doctor and one of Sarah. On Earth, several officials at the real Defence Station, including Colonel Faraday and John Benton had already been replaced with androids, their counterparts being aboard Crayford's XK-5 space freighter where Styggron also was, hoping to be protected from the contagion.
The Doctor, who uncovered the androids with his robot detector, had Grierson, a worker at the station, realign the radar dishes so that they pointed towards the base. The Doctor activated them, disabling the androids. Styggron was killed by his own virus. (TV: The Android Invasion)