The 456

The 456 (pronounced "four-five-six") was an alien race that negotiated secretly with the British government in 1965, and again in 2009. This designation was given to them by humans based on the radio wavelength they used, and they took on the name as their own in their dealings with humans, as opposed to offering the actual name of their species, if any ever existed.

As they later revealed, they were drug addicts. The 456 used children as "the hit" because the bodily chemicals they create "felt good".

Biology
Humanity knew very little about the 456's biology and anatomy, as they only had contact with one member of the species, who remained within a nearly opaque gas, contained within a transparent chamber. The natural design of their body consisted of three "heads", connected to one body via three long necks. (TV: Children of Earth: Day Four) The 456 thrived in an atmosphere made up of 25% nitrosyl chloride, 22% hydrogen chloride, 20% nitrogen, 12% fluorine, 9% hydrogen cyanide, 6% acetone, and 6% phosgene. (TV: Children of Earth: Day Two)

It was later revealed by the creature itself that the individual may have been under the influence of a recreational drug the entire time, the effects of which were not fully known. The 456 ambassador emitted a viscous green fluid in moments of frustration; this may have been an effect of either the use of recreational drugs or a natural response. (TV: Children of Earth: Day Three) Their blood was red (though this may have been from the human child connected to the individual). (TV: Children of Earth: Day Five)

Technology
The 456 had technological systems which could match the systems of the human race from 1965 onwards, such as radio telecommunications. They spoke English fluently and understood it perfectly; this may or may not have been through the use of a translator. They seemed to be far more advanced than the human race, indeed far more advanced than most other species, having the chemical and biological knowledge to provide a range of viruses and anti-viruses to humans. (TV: Children of Earth: Day Four)

The 456 arrived on Earth in what was described as a pillar of fire, allowing them to teleport into a specially made tank, despite it being within a building. When the pillar of fire appeared, clouds would gather around it and then dissipate once the pillar was gone. This pillar of fire appeared to do no damage to Thames House despite passing through at least the roof. UNIT believed that their base of operations was somewhere in orbit around Earth, but they were unable to find their ship, suggesting that the 456 possessed advanced cloaking technology. (TV: Children of Earth: Day Four) After the apparent death of the 456 ambassador, the 456 teleported his remains out in a similar way, with the remains disappearing into the sky in the form of a pillar of fire streaking upwards from Thames House instead of down into it. (TV: Children of Earth: Day Five) In 1965, the 456 took the children using a different method involving them walking into a bright light that disappeared in a flash rather than a pillar of fire. (TV: Children of Earth: Day Four)

They could also manipulate the minds of millions of children at will. When they came to Earth in 2009, they forced all children globally on Earth to chant "We are coming". The transmissions became more and more sophisticated with each sending, until the 456 manipulated each country's children into relaying a different message to their governments. Children around the globe communicated in English only, due to the 456's previous dealings with the British government. Through this connection, they could also give off a fatal signal, which they used to kill Clement McDonald. (TV: Children of Earth: Day One, Children of Earth: Day Four) However, if reversed in a constructive wave, the frequency was deadly to the 456, making their bodies exhibit extreme pain before violently exploding. As well, the 456 using the children in this way made them vulnerable to someone using the children as a transmitter in reverse to broadcast the deadly signal to the 456. (TV: Children of Earth: Day Five)

Culture
The 456 used human children as a source of drugs. They would forcibly attach a child to their body with a life support system. This allowed the child's chemicals to stimulate feelings of pleasure in the 456. During the process — according to the ambassador — the child felt no pain and lived long beyond its natural lifespan. However, it was conscious throughout the experience and had to use a respirator to survive in the toxic atmosphere. The entire reason for their visits to Earth were to get more children for the drug the children supplied them. (TV: Children of Earth: Day Three, Children of Earth: Day Four, Children of Earth: Day Five)

The real name of the species, if any existed. is unknown. In 1965, they didn't give the human race a name when making a deal. In 2009, after confirming that humanity's name for them was 456, they chose to go by that name, suggesting that they purposefully avoided giving away any sort of detail about themselves. (TV: Children of Earth: Day Three, Children of Earth: Day Four) This is further suggested by the 456 instantly removing any remains of the 456 ambassador following his apparent death, denying the human race the chance to study the remains or even confirm the ambassador's death. (TV: Children of Earth: Day Five)

Though the 456 possessed the ability to communicate through radio waves, they chose to take over the children of Earth to send their messages. Dekker suggested to John Frobisher that this was simply "because they could" and to act as a scare tactic for the human race in advance of their arrival. (TV: Children of Earth: Day Two) This tied in with the 456's tactics of using threats and intimidation to get what they wanted.

When approaching the human race for children in both 1965 and 2009, the 456 asked for them as a "gift" in exchange for their help. In 1965, the 456 offered something of equal value in return, but did not do so in 2009. Instead, the 456 issued threats if they did not get what they wanted. Gwen Cooper suggested that the visit in 1965 was the 456 essentially setting up a "protection racket" to prepare for their eventual return and greater demands. (TV: Children of Earth: Day Three, Children of Earth: Day Four)

The 456 chose to act through a great deal of shock and awe tactics. Along with using the children of Earth to send their various messages, they used a giant pillar of fire that was visible for miles around for teleportation. (TV: Children of Earth: Day Three, Children of Earth: Day Five) When Captain Jack Harkness threatened war between the human race and the 456, the 456 ambassador released a deadly virus into the atmosphere of Thames House to kill dozens of people and demonstrate how deadly a war between humanity and the 456 could be. (TV: Children of Earth: Day Four)

However, despite their high level of technology and deadly demonstration, the 456 chose not to pursue a war with or the extermination of the human race as threatened when they were defeated. After an attack that apparently killed the 456 ambassador, the 456 removed his remains from Thames House and retreated without any form of retaliation for either the apparent death of the ambassador or the human race's ultimate defiance to their demands. Ultimately, the 456 preferred intimidation and threats to all-out war and when faced with such, chose retreat rather than battle. (TV: Children of Earth: Day Five) In this way, the 456 were similar to the Monks who possessed advanced technology but retreated without a fight when the human race, aided by the Twelfth Doctor, defeated their invasion years after the 456 incident. (TV: The Lie of the Land)

First contact
The 456 first made contact by radio on the wavelength sometime during or prior to 1965. The 456 had learned English and knew something of Earth culture.

In 1965, Andrew Staines, Ellen Hunt, Michael Sanders, and Jack Harkness executed a deal with the unseen aliens. In exchange for twelve human children, the 456 gave them an anti-virus for a mutated strain of Indonesian influenza, which would otherwise, according to the aliens, have killed millions. These projections were agreed to by British analysts. The 456 claimed that the children would not be harmed, and in fact "would live forever" and that the 456 would not return to Earth. (TV: Children of Earth: Day Three, TV: Children of Earth: Day Four)

Twelve orphans were taken from the Holly Tree Lodge orphanage under the pretence that they were to go to another orphanage called Harbour Heights. These children were brought to a location in Scotland, where they were ushered into a white light. For unknown reasons, the 456 decided to leave behind one orphan, Clem McDonald, who ran off alone into the night. Torchwood Three later speculated that they weren't interested in him because he was on the brink of puberty. (TV: Children of Earth: Day Four)

Initial contact
In September 2009, the 456 sent a message through every child—ages five to eleven—on the planet: "We are coming." (TV: Children of Earth: Day One Children of Earth: Day Two) They followed with detailed instructions sent secretly to Dekker for a purpose built, gas filled chamber to be constructed for them on Floor 13, the top level of Thames House, MI5's headquarters in London and the most secure building in Britain. Technicians set about constructing the containment facility before the aliens' arrival. (TV: Children of Earth: Day Two)



Arrival
On their arrival day, an ambassador transported itself from the sky in a pillar of fire into the chamber, and began negotiations with John Frobisher, whom Prime Minister Brian Green had had appointed informal ambassador. They insisted on addressing all the major powers, but Frobisher was able to convince them to keep quiet about the earlier dealings with the British government in 1965. The 456 asked for a "gift" of 10% of the world's children, in exchange for not destroying the human race. (TV: Children of Earth: Day Three)

The request was denied and the UK government offered sixty-seven hundred children of Failed Asylum Seekers; the 456 rejected this offer and used the children of each country to tell the respective governments the number of children required by the 456.

The arrival of Jack Harkness led to an argument with the 456, who released a virus into the air of Thames House as a demonstration of what the people of Earth would get if they didn't comply. This killed almost everyone in Thames House, including Ianto Jones and temporarily Jack Harkness. With no other choice, the governments of the world reluctantly agreed to the 456's demands, now seeing fighting back as useless. (TV: Children of Earth: Day Four)

Resolution of the crisis
Now represented by Colonel Augustus Oduya of UNIT, the governments of Earth conceded to the demands of the 456 and began collecting the children. In particular, the government of the UK began using the children from the lowest performing schools in the country. At Colonel Oduya's request, the 456 ambassador revealed that they were drug traders, seeking the children of Earth for the "hit" the children's chemicals gave them.

As the children were collected, Alice Carter convinced Johnson to work with Jack Harkness to defeat the 456 and to save the children of Earth. Jack realised that the signal the 456 used to kill Clement McDonald was new and if he turned it into a constructive wave, it could be used to defeat the 456. Jack used the children of Earth as one giant transmitter to send the signal to the 456 with his own grandson acting as the prime transmitter. The transmission caused the 456 ambassador to writhe in pain before appearing to violently explode. Immediately afterwards, the ambassador's remains were removed from Thames House in another pillar of fire. With the apparent death of their ambassador, any surviving 456 retreated from Earth rather than retaliate. (TV: Children of Earth: Day Five)

The 456 would become the namesakes of various resolutions and changes to laws across the globe, including the 456 Regulation in Great Britain and the 456 amendments to U.S. Code 3184. The 456 Regulation declared the members of Torchwood Three officially deceased, and the 456 amendments allowed the extradition of the Torchwood team into the United States when captured. (TV: The New World)

Behind the scenes

 * Their concept of living in a nearly opaque gas is similar to the Rill but they are not stated to be related.
 * Humans used the name "456" to refer both to the Ambassador and to the species generally.
 * The loud screech made by the 456 was previously used by the Nestene Consciousness in Rose and the Swarm in the Planet of the Dead.