“In any case,” I said, “I vote we don’t push to find out how far his authority extends.”

Molly reverentially handed a mug of hot chocolate to Nightingale. “Thank you,” he said.

“What about mine?” I asked.

Molly held up Toby’s lead and wagged it at me.

“Not me again?”

“I’m on bed rest,” said Nightingale. “Doctor’s orders.”

I looked down at Toby, who was crouched half hidden behind Molly’s skirts. He gave me an experimental yap.

“You’re not making any friends around here, you know,” I said.

DR. WALID let me watch while he fed my father into the MRI scanner at UCH. He said it was a 3.0 Tesla machine, which was good, but that really the hospital could do with another one to cope with the demand.

There’s a microphone inside the tube so you can hear if the patient’s in distress—I could hear my dad humming.

“What’s that sound?” asked Dr. Walid.

“Dad,” I said. “He’s singing ‘Ain’t Misbehavin’.’ ”

Dr. Walid sat down at a control desk complicated enough to launch a satellite into low earth orbit or mix a top-twenty hit. The magnetic drum in the scanner started to rotate with the sort of banging sound that makes you drive your car into the nearest garage. It didn’t seem to bother my dad, who carried on humming, although I noticed he did shift his rhythm to match the machine.

The scans went on for a long time, and after a while the microphone picked up my dad’s gentle snoring.

Dr. Walid looked at me and raised an eyebrow.

“If you can go to sleep while my mum’s on the phone,” I said, “you can pretty much sleep through anything.”

When they’d finished with my dad, Dr. Walid turned to me and told me to strip off and get in the machine myself.

“What?”

“Simone was probably feeding off you too,” he said.

“But I don’t play jazz,” I said. “I don’t even like it that much.”

“You’re making assumptions, Peter. The whole jazz aspect may just be a boundary effect. If your lady friend is an uncharacterized category of thaumovore then we can’t know what the mechanism is. We need more data, so I need you to stick your head in the MRI machine.” He put his hand on my shoulder. “It’s for science,” he said.

There’s something uniquely claustrophobic about sliding into an MRI scanner. The rotating magnets are on an industrial scale and generate a magnetic field sixty thousand times that of the earth. And they feed you into it wearing nothing but a hospital gown that lets a breeze flap around your privates.

At least Dr. Walid didn’t make me wait around for the results.

“This is your dad’s,” he said. He pointed to a couple of dark gray smudges. “Those look like minor lesions, probably hyperthaumaturgical degradation. I’ll have to refine the image further and make some comparisons to be sure. This is your brain, which is not only pristine and unsullied by thought, but also showing no sign of any lesions.”