The Sacrifice is the fourth book in the series. It was released 20th September, 2012.
In an interview with the author, Higson stated that it will focus on Small Sam and The Kid and also on Matt's religious scheme. In March, Higson said that Puffin offered him "a seventh book". This means, the direct sequel to The Enemy is now book five, with book seven becoming the book containing the final battle.
The story picks up after Small Sam's arrival at the Tower of London. We get some insight into how Jordan Hordern is running it. A boy called Brendan is sent to exile by Jordan because he stole food. Sam is restless, wanting to go out and find Ella, whom he heard went to Buckingham Palace. Ed doesn't want him to go westwards (towards the forbidden zone or no-go zone) and tells Sam to wait until DogNut gets back with news about the centre of London.
Meanwhile Shadowman is spying on the group he calls The Fear, noticing their new signs of intelligence.
Ed finds a girl named Tish in a building surrounded with sickos and helps her but accidentally kills her friend Louise while trying to save her. He notices she wears only green.
Sam and The Kid hear about The Lamb and The Goat, Mad Matt's stories. Sam and The Kid start training and fitting in when Tish turns them against Ed and the others who live in the tower by saying they will never let him go and look for his sister and that they want him to stay there. She proclaims that she and her friends that died while trying to clear the areas of Sickos and they went too far but that she lives in Trafalgar Square in a safe place they call The Temple. She says she knows the people from Buckingham Palace and that his sister is there and she will take him there. They make a plan.
Some of Ed's crew found cars with petrol and they were admiring them when Tish sets one on fire as a diversion. Sam has second thoughts but travels on with The Kid and Tish through the no-go. Sam feels guilt as he feels as though he betrayed the other kids. As they move on, they notice a strange sound, a clicking sound. The Kid recognises this place and they are soon ambushed with sickos. The Kid saves them and shows them down the way to a tunnel, leading to St Paul's Cathedral. As they get out they are faced with a gate, sickos have ambushed them again however and Sam and The Kid are trying to kill some sickos while Tish is trying to call for help. The kids from St. Paul's Cathedral save them and it is revealed that Tish's goal was to lead Sam to Mad Matt since he is the chosen Lamb.
Shadowman encounters a group of kids known as Jaz, Ricky and Johnny. They don't believe Shadowman's warnings about the Fear and end up being surrounded. Ricky quickly gets hurt in the leg and eaten. Jaz, Johnny, and Shadowman escape to a car but have lost the keys. Shadowman has to go back outside to get the keys off of Ricky's corpse. Once he comes back Jaz won't let him get in the car and he has to wrench the door open. Jaz gets injured by Bluetooth in the process then proceeds to crash the car. Shadowman falls unconscious.
When Shadowman wakes up he finds himself in an IKEA. Johnny crawled back to his friends and got help despite being injured himself. Jaz died of blood loss after the crash because a sicko chewed her foot off. The leader of the IKEA group is Saif who doesn't like Shadowman and acts too cocky for his own good. He leads his group of kids into an ambush the Fear had created. Only a few of the kids escape. Shadowman sees this from the top of a crane and begins to go back into the centre of the city to warn the others about the Fear. As he is moving he becomes pursued by Bluetooth and a pack of other adults.
Back at the Tower, Ed decides that he is responsible for saving Sam and the Kid and leads a group of kids through the no-go zone into town. His group includes Kyle, Macca, Will, Hayden and Adele. They encounter sickos with a grey jelly-like substance. Eventually, Ryan Aherne and The Hunters bring them to Parliament where Nicola tells them that she knew of DogNut but hasn't heard from him since he first came through. One of Nicola's kids, Bozo, tells the Tower kids how to get into St. Paul's and so Ed and company march into the settlement to rescue Sam and The Kid.
Meanwhile, Sam is being treated to a feast with the weird Cathedral kids. The Kid makes a friend out of a young violinist named Charlotte but is then thrown into a cage. Sam pleads for his friend's life and Matt gets confused. To see who is the real Lamb and who is the Goat he gives them a test. The Kid outwits Matt and says that he is the Lamb, making him look like the Goat pretending to be the Lamb. The Kid is put into a cellar with a sicko by the name of Wormwood. Wormwood can still talk and rambles on to The Kid. The Kid convinces Wormwood not to eat him and starts an escape.
Ed finally arrives at the Cathedral with his group from the Tower and storms in to save Sam and The Kid. His group fight off the sickos who have invaded the Cathedral but Adele, Tish and Brendan all die. The Kid convinces Ed to bring Wormwood along with them as he has influence over the other sickos. Farther into the city Wormwood notices his fellow adults chasing a 'fly.' This turns out to be Shadowman and Ed's group help him kill off the last of the adults chasing him, including Bluetooth. Shadowman reveals that his real name is Dylan and brings them to an old drinking club he had made into a base.
The end of the book shows that the Tower kids and Wormwood have decided to go to the Natural History Museum the next day. There are also short parts from David's, Nicola's and Ryan's points of view.
- Small Sam - A nine-year-old kid mentioned from The Enemy who escaped from Arsenal Stadium.
- The Kid - A nine-year-old kid mentioned from The Enemy who helps Small Sam escape from Nick and his wife, Rachael. Small Sam's best mate.
- Ed Carter - The right hand man of Jordan Hordern the leader of the Tower of London mentioned in The Fear.
- Jordan Hordern - A strict leader of the Tower of London who sentenced Brendan to exile because he stole food from the Tower of London.
- Brendan (deceased) - Boyfriend of Jessica who was mentioned in The Fear, who was sentenced to death by Jordan Hordern, but escapes to St. Paul's Cathedral and meets Mad Matt, Archie Bishop and their followers. Tells about Small Sam and The Kid.
- Wormwood aka The Green Man - A sicko who is far more intelligent than St. George and the gym bunnies. He can even talk, but barely understandable. Knows the origin of the disease.
- Mad Matt - A kid who is suffering carbon monoxide poisoning. Created a new religion of the "Lamb" and its shadow, the "Goat". Believes that the Goat must be sacrificed in order for the Lamb to be free from its shadow. Believes that Small Sam is the Lamb and The Kid is the Goat.
- Archie Bishop - One of the followers of Mad Matt and his right hand man.
- David King - A power mad kid who wants to dominate whole London and wants to demolish the crew from the Tower of London.
- Jester - David King's right hand man. Betrays many people and is sly.
- Nicola - David's love interest and wants to dominate whole London, also. The leader of House of Parliaments.
- Tish (deceased) - A girl who persuades Small Sam and The Kid to go seek for Small Sam's little sister, Ella, but brings them to the Cathedral where Mad Matt waits. Killed in the battle of Wobbly Bridge.
- St. George - A clever sicko and the leader of "The Fear". Able to control other sickos.
- Bluetooth (deceased) - A clever sicko and the general of "The Fear". Killed by Shadowman by decapitation.
- Shadowman - Tracks down "The Fear" and is waiting for revenge towards Jester.
- Jaz (deceased) - A girl who Shadowman meets during tracking down "The Fear". she dies after suffering blood loss from losing her foot.
- Johnny - Part of Jaz's group.
- Ricky (deceased) - Part of Jaz's group, killed after being pulled into the Fear when his group were ambushed.
- Will - A boy who joins Ed's team on his search for Small Sam, he has good eyesight.
- Macca - A boy who joins Ed team on his search for Small Sam, he owns a crossbar.
LIST OF DEATHS IN ORDER: