In the original 1953 BBC serial version, Carroon and two other astronauts are selected to test a new rocket designed by Professor Bernard Quatermass. The rocket in question, Quatermass 1, vastly overshoots it's intended trajectory and is presumed to be lost in space. However, it somehow swings back around to Earth and crashes in Wimbledon, England.
When the rocket is recovered, Quatermass and his team are shocked to discover that only Carroon remains inside, despite the others' spacesuits being present and there being no indication that the door was opened during flight from the black box recording.
Carroon, gravely ill, is taken into care by Dr Briscoe, who had an affair with his wife. Carroon quickly finds himself under the spotlight to explain the disappearance of his colleagues, not only to Quatermass, but also to journalists, Scotland Yard, and even to govornment agents when a group of agents working for a foreign power attempt to abduct him.
Quatermass is among the first to notice marked differences in Carroon's physiological and psychological states. When Carroon seems to display traits and thought analogues concurrent with the missing astronauts, Quatermass comes to the conclusion that an alien organism absorbed the other crewmen and is inhabiting the body of Carroon, slowly metamorphosing him into a plant-like organism, the spores of which his analysis conclude have the ability to bring about the end of all life on Earth.
The now rapidly-transforming Carroon is chased across London by police and seeks shelter in Westminster Abbey, where he is spotted by a BBC News crew. The armed forces are mobilised to contain the creature but Quatermass successfully appeals to Carroon and the others' remaining humanity and they turn against the creature from within, destroying it.
Hammer's 1955 UK/US film remake had a somewhat different ending; rather than attempt to reason with the creature, Quatermass kills the Carroon creature via electrocution.
Carroon is only ever mentioned twice in the rest of the Quatermass series, in the Quatermass 2 BBC serial and The Quatermass Memoirs audio drama.