But no amount of pulling seemed to get the window any further open. As Cat left off, panting, Tonino hammered the lower half of the window with his fist and shouted at the next pair of buckled shoes that walked past.

“Help! Help! We’re shut in!”

The feet went by without pausing.

“They didn’t hear,” said Cat. “It must be a spell.”

“Then what do we do?” Tonino wailed. “I am so hungry!”

So was Cat. As far as he could tell, it was at least teatime by then. He thought of tea going on at the castle, with cress sandwiches and cream cakes – Hang on! What castle? But the flash of memory was gone, leaving just the notion of cress sandwiches, luxurious ones with all the crusts cut off, and cakes oozing jam and cream. Cat’s stomach grumbled and he felt ready to wail like Tonino. But he knew he had to be sensible, because he was older than Tonino.

“He said we could have food when we’d cleaned the whole room,” he reminded Tonino. “We’d better get on and finish it.”

They climbed down and set to work again. This time, Cat tried to organise it properly. He made sure they worked only in short bursts and he found two not-so-broken chairs so that they could sit on them and rest while the latest lot of dust was sucked away out through open window. Slowly they worked their way towards the far end of the basement. By the time the light filtering in past the dirt on the window was golden, late evening light, they were ready to start on the end wall.

They were not looking forward to this. From ceiling to floor, that end was draped in a mass of filthy, dust-hung cobwebs at least two feet thick, fluttering and heaving, grey and sinister in the small draught from the window. Under the draped webs, they could just see another of the splintery work benches. On it, in the very middle, there seemed to be a small black container of some kind.

“What do you think that is?” Tonino wondered.

“I’ll see. More old rubbish, I expect.” Cat shudderingly put his left hand through the cobwebs, hating the sticky, tender touch of them, and took hold of the black thing.

As soon as his fingers closed round it, he had a feeling it was important. But when he had pulled it gently out, avoiding touching the cobwebs where he could, it was just an old black cannister with a round hole clumsily punched in its lid. “Only a tin tea caddy,” he said. “It looks as if someone’s tried to make it into a money box.” He shook it. Something inside rattled quite sharply.

“See what’s in there,” said Tonino. “It might be valuable.”

Cat pried at the lid, getting a big new patch of black dirt on his front as he did so. The tin was coated in generations of sooty grease. But the lid was quite easy to move and came off with a clatter. Inside were a very few red kidney beans. Seven of them.