He was. Marcellus had just sent Septimus on an errand and he had been about to check on the Fyre Cauldron while he was away. Time was ticking by.

“Thank you for coming at such short notice, Beetle,” said Marcia.

“He is not the only one who has come at short notice,” Marcellus observed tetchily.

“Beetle has not brought it upon himself, Marcellus. Unlike you,” Marcia riposted. Keeping her gaze on Marcellus she said, “Beetle, perhaps you would like to show Mr. Pye the Vent cooling system.”

By not even a twitch of a muscle did Marcellus betray any familiarity with what Marcia had said. His studied expression—seventy percent annoyance, twenty-five percent bemusement, five percent boredom—remained the same.

Beetle took the gleaming white piece of paper out from his folder and laid it in front of Marcellus, who looked at it with no more than a natural curiosity. “What is this?” he asked politely.

Marcia stabbed her finger onto the title. “Vent cooling system,” she read out very deliberately. “As you know, Marcellus.”

Marcellus picked up the sheet of paper and perused it. “How strange. It looks just like a spider’s web.” He looked up at Marcia. “And why do you think I know about this”—he glanced deliberately down at the title—“vent cooling system?”

Marcia fought down her mounting irritation. She had expected Marcellus to cave in when confronted with the diagram, or at least look guilty. Either he was a very good actor or this actually was nothing to do with him—Marcia was not sure which. She stabbed her finger at the scrawled note at the foot of the page.

“Because, Marcellus, you have written on it. There!”

Very slowly—playing for time, Marcia suspected—Marcellus fished out his little round spectacles and put them on, carefully fitting the curled earpieces behind his ears. Marcia tapped her foot impatiently.

Marcellus peered at the note. “Julius FYI—Vent Cooling System. M,” he muttered. “FYI . . . strange name.” Beetle began to correct Marcellus, but Marcia held her hand up to stop him. Marcellus looked up at Marcia. “And no doubt you think that the ‘M’ is for Marcellus?”

“Yes,” said Marcia. A waver of uncertainty wandered into her voice.

Marcellus scented victory. He smiled and put the paper back down on the desk. “Well, I do hope you don’t call me out to inspect every little note in the Castle signed with the letter ‘M.’ I shall be spending all my time going up and down Wizard Way. There must be so many notes out there from . . . let me see now . . . Milo, Morwenna, Marissa, Maureen, Marcus—”

Marcia blanched at the mention of Marcus. Marcus Overland, ex-Ordinary Wizard, had once been given Marcia’s ExtraOrdinary Wizard robes by the Wizard Tower laundry in error. He had paraded around the Castle in them, acting very badly indeed. There were still people who were convinced that Marcia had once run screaming down Wizard Way, waving a large pair of bloomers above her head. “That’s enough of that, Marcellus,” Marcia told him. “There is no need to be sarcastic.”

“I was merely pointing out the infinite possibilities of the letter ‘M,’” said Marcellus.

Beetle watched with a mixture of admiration for Marcellus’s cool head and annoyance at how Marcellus was putting Marcia off. It was time for some straight talking. From his folder he took a translucent piece of paper on which he had marked the position of all the puddles, and placed it on top of the Vent diagram.

“We had hoped you might be able to help us, Marcellus,” he said smoothly. “For the last few weeks I have been monitoring a very strange occurrence. Puddles have appeared throughout the Castle.”

Marcellus looked genuinely surprised, and then—Beetle was sure—a brief flash of panic crossed his face. Feeling more confident, Beetle continued, “At the beginning of the Big Freeze we had nine. My scribes have been checking on them daily and despite temperatures well below freezing, they report that no puddle has frozen over. And then two days ago four more were reported. Two appeared in scribes’ back gardens, and two in iced-up alleyways. It is odd, don’t you think?”

“I suppose it is,” said Marcellus. “But I don’t know why you are telling me.”

Beetle pointed to the papers lying in front of them. “You will see that on this top tracing paper I have a map of the Castle. On it I have placed a red dot where each puddle is.” Beetle looked up at Marcellus. “There are thirteen in all.”

There would be, thought Marcellus grimly. “Indeed?” he said coolly. “Is thirteen significant?”