The great steam clock on the landing wall struck midnight. Xandra and Lex had been ready and waiting, listening for the chimes. On the final stroke of twelve, Lex turned the skeleton key in the lock and opened the door.

With great care and as little sound as they could manage, the siblings crept out into the corridor and onto the stairs. Lex took the lead. Xandra grasped the banister and leant heavily on it as she climbed down. She had been practising her walking from the moment the armadillos had left them alone. But she was still aware of how new this process was to her. She wanted to make sure she didn’t fall down the stairs.

In the entrance, they stopped and listened. Apart from the hiss of steam from the clock, all was silent.

They made their way around the back of the stairs, along the hall and into the kitchens. The main room consisted of a long central bench, with ovens on one wall and cupboards on the other. There was an opening on either side, one leading to the walk-in pantry, the other to a washing-up room.

Passing a bowl of fruit on the bench, Lex snatched up an apple. He bit down on it and held it in his mouth as he used the skeleton key on the back door.

‘You had a huge dinner,’ whispered Xandra, as Lex closed the door behind them.

Lex shrugged as he chomped on a mouthful.

Xandra gazed up at the smattering of clouds hiding the moon.

‘Now what do we do?’ asked Xandra.

‘Wait … I guess,’ said Lex, bits of chewed up apple falling from his mouth.

Xandra’s thoughts wandered back to the Crystalline Palace. Perhaps she could get Archie to take them there.

‘Pssssst!’

‘What was that?’ asked Xandra.

‘Pssssssssssst!’

‘Did you hear that?’

‘It came from over there.’ Lex pointed into the darkness.

They strained to see and then they spied a shape bobbing about in the gloom. As it came closer, they could see that it was the pale tawny fur of Archie’s head and face. The rest of him was dressed in black and difficult to see.

‘This way,’ he instructed.

They followed him across the manicured lawn, past the clipped hedges and through the flowerbeds to the stone wall at the end.

Xandra realised that the wall was much higher than it had appeared from her window. She wasn’t going to be able to climb up that.

‘Hello!’ came a voice from above, and then a rope ladder dropped down in front of her.

‘Courtesy of Miss Tesla,’ said Archie.

‘Cool,’ said Lex.

Examining the ladder, Xandra shivered – a mix of nerves and the chill night air.

‘I’m not sure I’ll be able to climb all the way up,’ she said.

‘Not to worry,’ assured Archie. ‘Your brother and I shall ascend first, then all you have to do is get onto the first rung and hold on. We shall pull you up and then lower you down the other side.’

Xandra watched Archie and Lex climb. Then she grabbed hold of the rope with both hands, and lifted first one leg and then the other, until she was on the ladder. She heard grunts and puffs from above as she was pulled up. Then a hand grasped her under one arm and a hoof under the other, and she was hauled onto the wall.

The wall was quite wide, so Xandra was able to lie on it as the rope ladder was repositioned.

‘Well done,’ said Tesla.

Blinking, Xandra realised that the coypu was standing right in front of her. She was dressed from head to toe in skin-tight black fabric and was almost invisible.

‘One should always dress for the occasion,’ Tesla said.

When Archie and Lex were ready, Xandra lowered her legs over the wall and flailed about until her feet found the ladder. And then she was lowered. Reaching the ground, she stepped back to watch the others.

Suddenly, an arm wrapped itself around her and a paw clamped over her mouth, pressing a cloth over her lips and nose. She was yanked backwards.

She tried to call out, but couldn’t.

She tried to struggle, but wasn’t strong enough.

She watched helplessly as shadowy figures pounced on Lex and Archie.

The cloth on her face was damp and smelled sickly sweet. Xandra felt dizzy and tried to keep her eyes focused.

As the clouds rolled clear of the moon, Xandra saw the figure of Nikole Tesla standing atop the wall, silhouetted against the sky.

And then her vision blurred and she lost consciousness.