Luella thought for a moment. “You’re a clever girl, no doubt about it, and you have a kind heart. I promise you.”

“You’re the only one who knows what happened to my brother. I want to find him, and I’m not sure how, but if I can unlock memories at least it’ll be a first step.”

Luella was silent for a while. Then she nodded. “So, you want to analyse my frequency as part of your search?”

“Yes.”

“Well, my dear, I feel this is a rather personal request, but it’s a noble pursuit indeed and I would be happy to play a small part in the process.”

In a moment, Prue had swept her up and hugged her close. “Thank you!”

Then Prue lay her equipment on the floor. “I want to attach a receiver wire to your chest, close to the qwortzite.”

Luella nodded. Prue gently inserted the wire, just a millimetre or two so as not to risk any damage, then she switched on the GODAR. It crackled, then she slowly twisted the dial. A frequency appeared on the screen.

“Well, I’ll be darned!” said Luella.

“Hold still, I’m going to make some notes.” Prue hurriedly sketched the shape in her journal. “Right, I’m going to zoom in a bit.”

Prue’s breath caught in her throat. There were complex patterns within the wave: waves within waves, within more waves. Some curved, another like saw teeth and another like a series of steps. She hurriedly copied it all into her journal.

“Will you move a wing for me, please?”

Luella did so, and the square wave contracted and expanded.

“Now could you imagine how it feels to fly?”

The saw tooth wave moved.

“Fascinating,” Prue breathed. “That must be linked to emotion.”

“I’ve no idea what you’re making sense of in all those squiggles, but I’m glad it’s of some use!” Luella laughed – and as she did so, the saw tooth signal rippled again on the screen.

Afterwards, Prue hid her journal back in the box and then popped her head out the door and checked the coast was clear before sneaking back out. She hurried to the mechanics laboratory for her lessons, and found apprentices of all levels were already there, bustling inside.

“Where have you been?” asked Edwin.

“Library.”

“That’s funny,” said Cora, “because the library is in that direction.”

Prue’s cheeks burned.

“And I thought you three were such good friends.”

Edwin and Agapantha went quiet and they all hurried inside.

“Why don’t you sit with me today, Agapantha? We both know we’re the only two who are going to make it here,” said Cora.

Prue ignored her and found a free seat. Master Tinubu was at the front of the class waiting.