“Crack!” came the sharp noise again. “CRACK CRACK CRACK!”

Dot shivered. It was a horrible sound – set her teeth on edge.

“FarView please Lucia!” said Walpurgis quietly.

Smoothly, with a kind of whining noise, a square sheet of what looked like see-through plastic on top of a shiny metal pole slid up out of the bottom of the boat, just in front of where they were standing. With a “zeeeeee” noise, it turned itself in the direction of the black cloud.

“Thanking you for FarView Lucia!” said Walpurgis, and the boat gave her little answering quiver.

Through the FarView screen, they could see what was happening as if it was right next to where Lucia was floating along, high in the blue and gold net-sky.

The sharp cracks were coming from a cloud - a deep, dirty black cloud, shot through with little squirming grey flecks. A bit yukky actually. It looked horrible, and dangerous. But round it, dipping in and out of its edges, flashing back, twisting and turning but never hitting each other, were little dark-blue, dart-like shapes.

“Vironators!” said Dot excitedly. “Exactly!” said Walpurgis. “They’ve grouped up some worms – one of the nastiest computer viruses, in my view – and now watch what they’ll do.” He peered more closely at the FarView screen. “Got some work in front of them, mind – I’d say there are about five billion worms in there!”

“More like ten, I’d say!” said Katzilow, who’d finished his rice and mushrooms and had come to join them, with a glass of something fizzy and nice-smelling in his paw.

Walpurgis opened his mouth to reply – but then caught sight of Carmeramalita smiling gently at him and shut it again.

“CRACK CRACK CRACK!” The Vironators were definitely hard at work – but they weren’t having it all their own way.

Suddenly one of the yukky little flecks in the cloud – Dot realized they actually looked like slimy white and grey worms – extended itself to many times its size, stretching out like the tongue of one of those amazing lizards that can catch flies as they whizz past.

It wrapped itself round one of the Vironators, oozing a sort of sticky slime as it did so. Dot gasped and Wiz barked his special “Let me have a go!” barks.

“Wormwrapped!” said Walpurgis excitedly. “But don’t worry – just watch what happens next!”

The long slimy grey thing was winding itself tighter and tighter round the Vironator – stopping it dead in the net-sky, though its white flame-like rockets at the back were still firing. You could still just see its number, near its front wing – VIR-1889.

Tighter and tighter the worm wound itself round the Vironator – so that it was soon almost invisible, as if some one had wound dirty, slimy grey string round it. All that could be seen now was its shiny pointy blue nose – and not much of that either.

The funny thing was though, the other Vironators didn’t stop to help. They just went on zooming and swooping around the cloud, as if they were keeping it in one place.

They reminded Dot of the amazing sheep dog trials that used to be on the BBC – she’d loved watching them with her Gran, who was a country girl at heart. The dogs were so clever grouping all the sheep together, just by listening to the special sounds and whistles made by the shepherd.

But now the Vironator caught by the worm had disappeared completely inside its slimy coils.

“Why do zey not help ze poor fellow?” asked Fromage, waving his arms about. “It is too bad!”

“Yes, not fair!” said Dot.

To her amazement, Walpurgis just chuckled. “Oh yes it is!” he said. “He’s winning - look now!”

And he was right! As they watched, the coils of the worm suddenly fell to pieces – hundreds of little bits of its slimy body scattering everywhere. But of the Vironator there was no trace! Nothing at all!