Clement McDonald

Clement MacDonald, simply known as Clem, or Timothy White in an English psychiactric hospital, was the only one of the twelve children not to be taken by the 456 after he was meant to in 1965. He would grow up in secret, until Torchwood Three took attention to him as he was chanting the same things whatever the 456 controlled all the children of Earth in 2009. He was known as "the Remnant" by the 456, who eventually "disconnected" him, resulting in his death.

First encounter with the 456 (1965)
He was born in Scotland sometime in the 1950s. An orphan, he grew up at the Holly Tree Lodge in the same country. In 1965, an alien race designated the 456 came to Earth to give the Human race an anti-virus to Spanish influenza which would wipe out millions of lives, in exchange for 12 children, as they give off certain chemicals that gave them the equivelant of a high from Earth narcotics. The government and the Torchwood Institute chose him and eleven others from his orphanage, since no-one would miss them, and hence keep this secret. After arriving in a secluded location, Captain Jack Harkness drove them to a white a light, and guided them from there. (TW: Children of Earth: Day Four) However, Clem was the only one who managed to escape. He was being chased for several miles until the 456 decided to stop. (TW: Children of Earth: Day One)

Since then, he was somewhat slightly connected to the aliens, and given sense of smell far beyond normal for an average human beings, as well as a physic ability. For the next four decades he would be haunted by Harkness's face, and was for unknown reasons submitted to a psychiactrict hopital in West Sussex, lost his Scottish accent and went under the alias of Timothy White as to not get detected by the government. (TW: Children of Earth: Day One)

Second encounter with the 456 (2009)
In September, 2009, the 456 returned and controlled every child on Earth to chant "we are coming"; Clem also chanted those words, the only adult known to do that too. This attracted the attention of Gwen Cooper from Torchwood Three. She took time to visit him on the first day of the 456 incident. After questioning "Timothy White", he was able to use his sense of smell to determine whe was telling the truth regarding that she worked to stop alien threats. He told her his actual story and that he can sense them coming (he didn't like their smell the closer to Earth they got), before discovering that she was three weeks pregnant. In shock, she left. Later, after being discovered by the British government, he was among those being targeted. When police arrived in the psychiactric hospital to arrest him, he was able to escape into the night. (TW: Children of Earth: Day One)

On the second day, he was seen in a pub near London, where his smell sense of the 456 grew even stronger; the people in the pub grew very suspicious of him. After they find out he has stolen a wallet, police arrived to arrest him after a brief struggle. (TW: Children of Earth: Day Two) By day three, he was released on bail by Gwen and Andy Davidson, and was brought to their makeshift base in London belonging to Torchwood One, after their hub was destroyed by the government. By the end of the day, he was haunted to see Harkness, who hadn't change a bit in 44 years. (TW: Children of Earth: Day Three)

In revenge and anger, he shot Jack dead, but was further stunned after Jack revived himself. Gwen was able to calm Clem down, and he was able to provide some assistance to the team again. Jack and Ianto Jones were able to get into Thames House to negotiate with the 456, who had arrived the previous day (they demanded 10% of Earth's children). When the 456 refused to go empty handed, it inflicted pain on Clem; the trauma caused internal bleeding to his body from his brain. Eventually, before it killed everyone inside Thames House, it "disconnected" him, effectively killing him in front of Gwen's eyes. (TW: Children of Earth: Day Four)

Theory
It was theorised he was spared because he was on the cusp of puberty, which may have rendered him useless to the 456. Although they seemed to have simply abandoned him, some measure of a two-way connection did remain.