Monday In Other Place. Did nothing. - Jonathan Stroud

The boy did the preliminaries, sealing the circles, erecting the bonds. Now we were all subject to the rules of the summoning. But then he stopped. He did not progress. The woman looked at him furiously. "I've forgotten it," he said.

Perhaps he'd want me to conjure up an illusion. That might be fun: there was bound to be a way of misinterpreting his request and upsetting him†.

The temperature of the room dropped fast.