On his part, Jax realised, his interest was more than morbid fascination. The Serpent was a riddle. He was unexplained. Unsolved – crazy was too convenient for Jax. And he wanted to solve the Serpent as much as he wanted to solve himself.

Jax stopped an inch away from the cell. It was only then he saw the erection. Arms by his side, his bulging scarified muscles covered only by tattoos and smeared blood, the Serpent was aroused and standing like a statue. He was staring at Jax.

Those eyes. Again. Cold. Dead. Crazy. Crowded.

The Serpent’s smile widened just before he turned away. He was pleased to have an audience, Jax thought. A witness to his ritual. Serial killers always crave attention, so the isolation and anonymity of prison are the biggest punishments of all. Maybe that’s why he’d cut himself. For attention.

Jax was wrong. He winced as the Serpent plunged his right index finger into the open wound on his left forearm. There was no explanation for this. Or so Jax thought – until the Serpent turned blood into finger paint.

He lifted his right hand towards the adjacent wall. On its surface was a mural of madness, a canvas of crazy. Jax had never seen anything like it. The wall was completely covered in graffiti. Maps, charts and equations. Arabic and Armenian. Dodgy doodles and detailed drawings. Genius and gibberish. Most of the marks had been made with chalk – blue, yellow and white – but the wall had also been scratched and incised, smeared with shit and splattered with blood.

In the middle of this mess five large numerals had been etched into the concrete.

‘Nine,’ the Serpent said as he traced the first of the numbers with blood.

‘Three,’ he said, moving to the second numeral.

He returned to the ink-well in his arm, sticking both his index and middle fingers in this time for a bigger serve.

‘Two,’ the Serpent continued as he methodically turned another numeral red.

He whispered as he worked. Jax could see his lips moving, but he couldn’t hear him properly again until the Serpent, fingers dripping with blood, shouted out the next number. ‘Four.’ It was bingo for the bonkers.

The neatness of the numbers unnerved Jax. Crazy was slashing and scratching. Jagged edges and all out of control. Not precision.

‘One,’ the Serpent said before stepping back to study his work.

93241.

The five numerals were dead centre in the middle of the wall. Viewing the whole wall now that the Serpent had backed away, Jax noted that the only significant space left on the chaotic canvas was a patch of clean concrete below the freshly bloodied numbers. It stood out like a beacon.

The Serpent turned.

The Serpent charged.