According to the ancient texts of the Karnas'koi, it was said that "three Lurkers dream in the vaults, with the Fourth Dreamer elsewhere in the shape of a man." CP Doveday was this fourth dreamer. He was an envoy created by the Karnas'koi and made to seem like a normal human being. He came to the surface with their crystal key and entrusted to reconnoitre Earth in advance of the Karnas'koi's second attempt at taking over the planet.
However, their plan did not entirely work, and the Seventh Doctor theorised that he was created "too human" and that the conflict between his humanity and the alien mind resulted in psychotic periods of hallucinations and recurrent blackouts. The stories in his book were largely a result of his dreams.
In 1934, he went to a New York City psychologist called Doctor Freya Gabriel. There he underwent hypnotic regression therapy where Gabriel and her recent colleague Professor August Corbin unravelled his true origins and created false human memories to subdue it. They realised that Doveday's Karnas'koi self was in telepathic contact with his kind, which the Doctor described as a Hive mind. They attempted to use CP to subdue the awakening Karnas'koi, removing him to a new Institute hospital on the island along with every copy of his published writing. (AUDIO: Lurkers at Sunlight's Edge)