The captain turned away to shout orders to his crew and the sailors hurried aloft to shake out the reefs in the huge mainsail. At the stern, the steersman strained at the tiller, turning the Horus towards the sunset.

'What is he doing?' asked Sempronius. 'The fool is heading straight for the wave.'

Cato nodded. 'Makes sense. The bows are the strongest part of the ship. If we meet the wave head on, we might break through it, if we can't ride over it.'

Sempronius stared at him. 'I hope you are right, young man. For your sake, my sake and all our sakes.

As soon as the senator had spoken, Cato's mind focused at once on Julia and he called to Macro as he hurried towards the gangway leading to the cabins. 'Get yourself tied to the mast, and take the senator with you.

'Where are you going?'

'To get Julia and Jesmiah. They'll be safer on deck.'

Macro nodded, then glanced towards the horizon, and now he could see the wave more clearly, rising up in a great bar that extended far out to sea, while the other end foamed and crashed along the coast. 'Be quick, Cato!'

Cato ran across the deck and jumped down the short flight of steps into the passengers' quarters, where thin stalls accommodated those who had paid the most for their passage to Rome. Thrusting aside the canvas curtain that formed the makeshift entrance to Julia's quarters, he ducked his head inside. Julia sat on the deck, cradling Jesmiah in her arms.

'Cato! What's the matter?'

'No time to explain.' He stepped towards her, stooped and drew her up on to her feet. Jesmiah scrambled up at her side, wide-eyed with terror.

'Master Cato,' her lips trembled, 'I heard someone say there's a monster.

'There's no monster,' he snapped, thrusting them both out of the stall and up towards the gangway. 'We have to get on deck, as quick as possible.

Julia stumbled up the steps towards the deck. 'Why? What's happening?'

With a quick glance at Jesmiah Cato replied, 'Trust me and do as I say.'

They emerged on to the deck in a scene of terror and chaos. Macro had tied the senator to the foot of the mast and was hurriedly doing the same for himself. All around the other passengers and crew were doing the best they could to secure themselves to the vessel. The captain had joined the steersman on the small steering deck and both men braced their arms on the tiller and stared grimly ahead.

Jesmiah stared round in horror and drew up.

Cato grabbed her arm and dragged her roughly towards the mast. 'Come on, girl! There's not much time.'