"Ellen," said Alice, the next set of doors opened. "That was..."

"That was great," said Alex. "Well done."

"Thanks, but it was really easy," said Ellen. "This is just the same as ancient 2D pinball. I could have done it quicker with fixed bumpers and some flippers, but it was just like playing multiball. It wasn't hard at all."

"You'll have to teach me how to play when we get home, your highness," said Captain Zachary, as they hurried across the board towards the fourth room. He glanced up at Chata and lowered his voice. "If we get home. This isn't just malfunctioning systems. She really is trying to kill us."

* * * * * * *

At the same time, Lord Blackstar, Will and Darla were walking out of their third room and into their fourth.

"It's really simple, Will," said Lord Blackstar. "A chessboard is eight squares by eight. That's sixty four squares in total. If you number each square – one to sixty four – it adds up to two hundred and sixty. It's basic maths."

"Oh, I see," said Will. "So that's how you did it."

"Yes, it's feature of chessboards that's been known about for thousands of years," said Lord Blackstar, looking up at Chata, who was glowering at him from the latest screen. "Anyone who can count could work it out. I'm starting to wonder if you're really as artificially intelligent as you claim to be, computer."

"I am," said Chata. "And don't get overconfident, Lord Blackstar. You are not nearly as intelligent as you think you are."

"I've been telling him that for years. It doesn't make any difference," said Darla.

"Be quiet, Darla," said Lord Blackstar. "And may I point out that I haven't let you down yet."

"No. I hate to admit it, but you've been doing very well," said Chata. "You've been almost as fast as Steven was. So I'm going to give you something different this time. Something that's going to challenge a different set of your skills."

"I'd prefer something that actually does challenge my skills," said Lord Blackstar, looking around the room. It contained another giant chessboard with blue and white squares, but this one was deserted. All the squares were empty. There were no chess pieces anywhere in the room. "But fine. Let's get on with it. What are we playing this time? Blind Chess? Invisible Chess? Reverse Haunted House Chess?"

"No. Something entirely different," said Chata. "If you'll wait just four more seconds, your opponents should be here right about..."

A large section of the wall exploded. Dust billowed into the room. Rubble and fragments scattered across the floor. Lord Blackstar, Will and Darla spun around.

"...now," said Chata.

"I don't care if you didn't bring enough, de la Vega! Spread it out. Make it last! We might well need it before the end," came a voice through the hole.

"Captain Mendoza?" said Will, as the Sirian team captain strode through the hole, waving the dust away.

"What? Good grief! Lord Blackstar!" he said. "You've made it this far as well. Congratulations."

"What are you doing?" said Lord Blackstar.

"Oh, the computer's obviously defective," said Mendoza, waving at Chata, as the rest of the Sirians came through the hole behind him. "She keeps setting us challenges that are physically impossible. We'd been forced to resort to progressing by hand."

"By which you mean that you and your teammates haven't won any of the games I've set for you so far, so you've been blowing holes through my walls instead," said Chata.

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