From TARDIS Index File, the free Doctor Who reference.
The Night Travellers were a travelling circus group in Britain in the late 19th and early 20th century. They only appeared at night and were said to "come from out of the rain" (suggesting that some kind of H2O Scoop technology was used. Alternatively, it could be said to be how they were described to appear from the darkness and blurriness of rain.). (TW: From out of the Rain). The Night Travellers stole people's breath. After travelling circuses fell out of fashion, all that remained of the Night Travellers were films tucked away in cupboards. When an old cinema reopened and one of these films was shown, the Ghostmaker and Pearl were freed. They set about taking the breath from people. They attempted to free the other Travellers and succeeded. They were defeated by being filmed once again, recapturing them on celluloid, followed by Jack exposing the film to the light and destroying them. Jack claims, however, that they could come back if there are other old film canisters containing them.