[1] The books are written from perspective of the teenage protagonist Alex Sawyer and describe his incarceration in the fictional London prison Furnace Penitentiary.

Convicted of a murder he didn't commit, sentenced to life without parole, ‘new fish’ Alex Sawyer knows he has two choices: find a way out, or resign himself to a death behind bars, in the darkness at the bottom of the world.

Soon Alex discovers that the prison is a place of pure evil: where creatures in gas masks stalk the corridors at night, where giants in black suits drag screaming inmates into the shadows, where deformed beasts can be heard howling from the blood drenched tunnels below waiting to kill.

And behind everything is the mysterious, all-powerful warden, a man as cruel and as dangerous as the devil himself, whose unthinkable acts have consequences that stretch far beyond the walls of the prison.

But as he starts to uncover the truth about Furnace’s deeper, darker purpose, Alex's actions grow ever more dangerous, and he must risk everything to expose this nightmare that's hidden from the eyes of the world...[4] Alex, Zee and Gary are on the loose in Furnace tunnels and caves but are eventually found by the warden, the blacksuits and their hounds.

In the pitch black hole, where all the worst nightmares come true, Alex and Zee manage to stay sane by communicating to each other by banging on the steel pipes and the frequent visits of Simon - he yanks them out of their cells and works with them and his friends in order to make an escape attempt: first through a steeple, later through the incinerator.

In the prison's underground mazes Alex and Zee discover the dark truth: the inmates are lab rats; the wheezers perform procedures on them in order to become blacksuits but these experiments sometimes fail so they're either turned into 'rats' which seek only for food and revenge or 'mutants', half rats half boys, who are harmless because they remember their old lives.

With the 'nectar', a dark liquid full of tiny golden flecks, in his veins, Alex starts to forget things - his life prior and in Furnace, his friends and even his name - and what's left is a cruel, merciless hatred toward the weak and a lust for power.

After a while, he starts to feel weak due to the lack of the nectar; without it he can either become a boy again or completely lose his mind and become a merciless killer, worse than a berserker, but Simon takes care of it.

After an attack of the infected in St Martin's Cathedral that Alex, Zee, Simon and Lucy survive, they are brought by Annabel and another soldier to a supposed safe place of PMCs, later revealed as the blacksuits.

After Cross' death, Alex's considered Furnace's right-hand man, therefore, Sam and some berserkers help him and his friends to escape.

With Panettiere and her army on their heels (they want to study Zee's immunity to the nectar), they spend the night in Alex's house, where he finds out that his parents haven't abandoned him as he remembers but have been trying to get him out of prison, and then they finally reach the island where Furnace is.

However, with his friends' support Alex ends it by killing all of Furnace's creatures, including Simon, through telepathic images of freedom and peace.

Despite his young age, he makes several bad choices that lead him to imprisonment: he becomes a bully with two other kids, a thief and a liar.

He is on the brink of insanity due to the nectar running through his veins, but with his friends' help he manages to stay true to himself.

He's immune to the nectar: to the warden in Death Sentence he's of no use (he is unable to be turned into a blacksuit), while the army in Execution is very interested in him (he could hold the key to the cure).

In Lockdown he acts as a guardian angel for Alex, although he is loath to admit it, and takes part in the escape plan until he is taken away in the blood watch.

Warden Cross - One of the main antagonists whose eyes are so full of madness, hatred and rancid glee that meeting them is like watching yourself die a million times over.

Having been born in Hungary in the 18th century - thereby making him over 300 years old as of the events of the story - and has experienced this enhanced lifespan due to his usage of the Stranger's blood, the base product of the nectar.

For centuries, he traveled across Europe, creating soldiers with his nectar in order to make a world in which there is only strength and equality.

At first he is aloof and shows no warmness to Alex even after he saves his life during a skirmish in the trough room but at the end repays the kindness by making him, Donovan and Zee a legitimate meal using leftovers in the kitchen.

Alex and Monty seem to be the only characters in the series who remembered their names after being turned by the nectar (excluding Warden Cross).

They completely lose their mind due to the pain caused by the procedure and are always in search for food, including human's flesh, and revenge against the blacksuits and the warden.