Severus came to the telephone in the library. Just as he was about to pick up the receiver, it rang on its own.
"Hello," he said into the receiver.
"Good evening, Mr. Snape," Lyall Mayer said from the other end of the line. "Please forgive my discourtesy. Your friend is with us."
"I know," Severus said calmly. "Put Irma on the phone."
"I'm afraid that can't be done. She is not at the manor where we met last time," Lyall said. "Please don't worry. She will be properly cared for. No one will be hurt."
"How am I supposed to trust you?" Severus asked.
"I think you have no choice but to trust me," Lyall said. "And compared to that young lady searching aimlessly, I can offer you more help."
"What can you tell me?" Severus asked.
"That depends on how much you know. If you have any questions, feel free to ask," Lyall said in the tone of a mentor.
"What happened in 1870?" Severus asked.
"About what?" Lyall asked.
"The aurora," Severus said.
Lyall was silent for a moment before saying, "The Franco-Prussian War was underway then. A group of Prussian spies infiltrated the city. I don't know whether their original purpose was to gather intelligence and they stumbled upon those secrets by accident, or whether they had come for those secrets in the first place. In any case, they caused trouble, and someone corrected their mistake to prevent Paris from falling into an even greater crisis."
"What caused the lake in Montsouris Park to dry up?" Severus asked.
"That was another mistake," Lyall said. "A traveler from Egypt poisoned the water in the Montsouris Reservoir for revenge."
"Who was it?" Severus asked.
"How did you learn about the aurora?" Lyall asked.
"I read someone's diary," Severus said.