I had a brand new set of keys, including one for the tradesmen’s entrance round the back. That way I didn’t have to sneak past the disapproving gaze of Sir Isaac. The main atrium was dimly lit, but as I climbed the first flight of stairs I thought I saw a pale figure gliding across the floor below.

You know you’re staying somewhere posh when the breakfast room is a completely different room and not the same place where you had dinner, only dressed up with different china. It faced south-east to catch the thin January light, and looked out over the coach house and mews. Despite the fact that only Nightingale and I were eating, all the tables had been laid and bore laundry-white tablecloths. You could have seated fifty people in there. Likewise the serving table sported a line of silver-plated salvers with kippers, eggs, bacon, black pudding and a bowl full of rice, peas and flaked haddock that Nightingale identified as kedgeree. He seemed as taken aback by the amount of food as I was.

‘I think Molly may have become a little overenthusiastic,’ he said and helped himself to the kedgeree. I had a bit of everything and Toby got some sausages, some black pudding and a bowl of water.

‘There’s no way we can eat all this,’ I said. ‘What’s she going to do with all the leftovers?’

‘I’ve learned not to ask these questions,’ said Nightingale.

‘Why’s that?’

‘Because I’m not sure I want to know the answers,’ he said.

My first proper lesson in magic took place in one of the labs at the back of the first floor. The other labs had once been used for research projects but this one was for teaching, and indeed it looked just like a school chemistry lab. There were waist-high benches with gas taps for Bunsen burners placed at regular intervals and white porcelain basins sunk into the varnished wooden tops. There was even a poster of the periodic table on the wall missing, I noticed, all the elements discovered after World War Two.

‘First we need to fill up a sink,’ said Nightingale. He selected one and turned the tap at the base of its long, swan-necked spout. There was a distant knocking sound, the black swan neck shook, gurgled and then coughed up a gout of brown water.

We both took a step backwards.

‘How long since you used this place?’ I asked.

The knocking grew louder, faster and then water poured from the spout, dirty at first but then clear. The knocking faded away. Nightingale put the plug in and let the basin fill three-quarters before closing the tap.

‘When you’re attempting this spell,’ he said, ‘always have a basin of water ready as a safety precaution.’

‘Are we going to make fire?’