Invasion (Adam)

In the 51st century, the human inhabitants of the Boeshane Peninsula lived under the threat of invasion. Ultimately, what Jack Harkness described as "the most horrible creatures you could possibly imagine", whose howls travelled before them, arrived. They had been known to pass over the Peninsula and it was believed that they would do so again, but it was on that day that they attacked. Jack's father, Franklin, had sent him away with his younger brother Gray to run for safety as he went to find their mother. As they ran, however, Jack lost Gray after losing the grip on his hand. Jack returned home to find his mother with Franklin's corpse. (TV: Adam)

Gray himself was captured by the creatures who, as he recalled, "lived to torture". They kept him and others just on the verge of life and he would lay, hemmed in by corpses, praying to become one. Years later, the now adult Gray sought retribution against his brother following these experiences. (TV: Exit Wounds)