And there they were - outside Colony Cerulean, where the Wisp of Mr Mouse might be.

It was quite cool once Lucia the Tracboat had settled on the ground of the Valley of Sleep - cool, with a faint breeze blowing. One by one the TricTrucTrackers jumped down from Lucia. Each carried a black backpack, with his or her name on it in green. Like a military patrol, they lined up smartly, with serious looks upon their faces.

Dot tucked Fromage into his cousin's hidey-hole spot under the collar of her T-shirt, picked up Wizard and tucked him under her arm, and jumped down too. The ground of the Valley gave slightly under her feet as she did so.

The tented walls of Colony Cerulean flapped in the breeze. The flag above it - a golden mouse on a deep red background - fluttered noisily, suggesting the wind at the top of the big tent was blowing more strongly than it was at ground level.

Dot remembered something she'd meant to ask.

“Why is it called the Valley of Sleep?”

Katzilow grunted as he slung his backpack over his shoulders. It looked quite heavy.

“Because all of the actions - the key strokes on a keyboard, the clicks of a mouse, all that - are over. Asleep” he replied. “But they still exist because they are part of that device's story. And they grow all the time, of course - and each action carries a clue about where that device is right now, what computer it's plugged into and where it is.”

Walpurgis signed off the Tracmapper, and jumped down too. “OK everyone!” he said “MiniTracs all ready for check-find?” The TricTrucTrackers all nodded. “I’ll check if you please!” He moved off down the line of his friends for his inspection.

Carmeramalita holding up her MiniTrac so Dot could see. It was a strange-looking thing – shaped like a pear, and about the same greeny-gold colour. The TricTrucTracker held it out. “Try it!” she said with a beaky smile.

Dot took it and found to her surprise that it was made out of the same squidgy material as Tracmapper keyboard. When the TricTrucTracker handed it over, she noticed that it had taken on the shape of her paw, like play-doh does when you squeeze it – but as Dot handled the device, it moved in her hand, and moulded itself to her. It made her jump a bit.

Then a little line of silver lights ran round the bigger end of it – you had to hold it with the thinner bit of the “pear”. It made Dot jump again!

Carmeramalita smiled. “It’s saying it doesn’t recognize you” she said. “Quite right too! All our MiniTracs are like that – so no-one else can use yours.”

“What does eet do?” asked Fromage, nervously stretching out his little claw towards the MiniTrac, but bringing it back quickly as it started to move in Dot’s hand to check him out too. It wasn’t a very nice feeling, thought Dot.

“It knows what we want to find” said the lady TricTrucTracker. “It will pull us towards your Mr Mouse, if his Wisp is inside Colony Cerulean.” The tent gave another flap in the net-breeze, as if it recognized its name.

“Like me tracking? Hic!” went Wiz.

“Yes, just like that” grinned Carmeramalita. “But it doesn’t do hiccups!” “Very funny!” muttered Wiz.

She took the MinTrac back from Dot, as Walpurgis came up. He peered at it closely, then nodded, shrugging his backpack on straight. “Right - we’re all ready!” he said. “Dot, Fromage, stay close to me please - it's like a maze inside these colonies. Now then, everyone! On my note!” He closed his eyes, threw back his head, and opened his beak. More singing!

“Dee da dee DA DEE DA” he went.

Well, humming really.

“Dee da dee DA DEE DA” replied the TricTrucTrackers.

“Voyez! Look!” said Fromage.

Once again the musical powers of the TricTrucTrackers were making things happen. As they watched, the edge of the tent began to lift up – as if were being pulled by an invisible string, right in the centre of its front wall. Higher and higher it went – with the TricTrucTrackers humming on – till an opening like an upside-down V had appeared in front of them. Rays of cerulean-blue light came shining out towards them, making everyone look like they were under a crystal-clear tropical sea.

As the light faded, Dot peered in through the opening - and her heart sank.

How would they ever find the Wisp of her friend in the middle of all that!!