Another wave threatened his equilibrium. He pushed it back.

‘Mother is busy running an important errand.’ Thanatos settled himself on his stone throne behind his long black desk. ‘Your silly little sleep trumpet will have to wait until tomorrow when she returns.’

‘It’s not silly,’ whined Hypnos. ‘You’re silly . . .’

‘So how do I put the flames out?’ said Elliot impatiently, not in the mood to hear the Daemon twins’ latest squabble. He looked around the dingy office, lit only by torches on the wall and the menacing glow of the river below. This place was grim. He couldn’t wait to leave. With Mum.

‘You don’t,’ said Thanatos crossing his long fingers.

‘Then how do I get the Fire Stone?’ snapped Elliot. ‘In case you haven’t noticed, I’m not exactly fireproof.’

‘Well . . . perhaps you are?’ Thanatos mused.

Elliot clenched his teeth.

‘Could you, just for once, give me a straight answer?’ he hissed. ‘You are epically annoying.’

‘Forgive me,’ said Thanatos slowly. ‘You recall Pythia’s prophecy? It refers to “a young mortal child with the heart of a lion”. Apparently, that’s you.’

Elliot shrugged. That same prophecy had also said that he could ‘conquer the world with the help of four stones’. He remembered that bit.

‘Well, now we’re going to find out for sure,’ said Thanatos. ‘Only the truly courageous can survive the flames of the Phlegethon. Your courage will protect you from the fire like a suit of armour.’

Elliot glanced at his burnt finger.

‘And how do I know if I’m truly courageous?’ he said.

‘You dive head first into the flames,’ said Thanatos. ‘The answer comes back pretty quickly.’

‘And if I do this, you will definitely give me my mum back?’ said Elliot uncertainly.

‘For the last time, I have sworn an oath on the Styx,’ Thanatos insisted. ‘If I break it, I will lose my kardia and become mortal. Quite aside from the sheer repellence of the idea, it’s not much use having power over the Earth and everything in it if I can be knocked down by a number 73 bus. I will return your mother’s soul, you lead it out of the Underworld, and, as soon as you reach the Earth, she will be restored to her mortal form, just as she was before she—’

‘I get it,’ Elliot interrupted, not wanting to hear the words said out loud. His mum wasn’t really – not living. She was coming back.

Elliot stood up and returned to the window. He watched wave after wave of flame ebb along the river. There was nothing he wouldn’t do to have his mum back. But what if he couldn’t?

The flames outside suddenly roared.

‘They can sense your fear,’ whispered Thanatos, lurching up over his shoulder. ‘You have to get it under control. Tiredness won’t help. I’ve been told you’re not sleeping.’