The Kid appears in The Enemy, the Sacrifice, the Fallen and The End as Small Sam's sidekick. He plays a major role in Mad Matt's religion as 'The Goat' a trickster who tries to mislead Small Sam (the Lamb in Matt's religion) but in the real world, this does not happen.
The Kid never seems to talk about his parents, although he does reference his Uncle and his Granddad when he talks about music, and Alberitch's cave. Not much is known about him. His first appearance is when he saves Small Sam from the butchers at Bank station, in the no-go zone. His real name is unknown however in the Sacrifice, while he is being whipped by Mad Matt, he says his name is Angus Day (this is part of Matt's religion) but it remains unclear whether he was lying or not. Throughout the series, he is referred to as the Kid unless he is being spoken to or about by Matt's religion, then he is referred to as the Goat. In the Sacrifice, while spending time at St Paul's, he is captured by Matt and fed to Wormwood (aka Mark Wormwold) but escapes and leads both himself and Wormwood to safety. After his experience in St Paul's, Ed Carter leads him, Small Sam, Charlotte and other members of Mad Matt's religion to the Natural History Museum, where Small Sam and the Kid stay until the end of the series. Charlotte also stays here with them but gets eaten by sickos in The End.
The Kid is a wacky character, who speaks in riddles and plays on words such as "That's because I'm elemental, my dear Watson". He seems to be very skilled, yet you wouldn't think it because the way he gibbers makes him seem insane. He often talks to himself. He also has great knowledge of underground places, this may relate to him being a lone explorer during his childhood but is unclear.
The Kid is described as having spiky hair, a women's leather jacket with no sleeves, a dress, and tartan trousers. People comment on this and say that he's weird. Even when he washes, his hair stays straight up and spiky.
The Kid is loyal to Small Sam to the point that he relies on Sam to make all the decisions. They never want to be apart. The Kid says at many points in The Sacrifice that he'll go with what Small Sam says, such as when they leave the tower. They argue sometimes, in a friendly way.
She spoke to The Kid when she wasn't supposed to at the Cathedral. She quickly made friends with him and followed him when they escaped the Cathedral with Ed and others.