"Do you have a tuning fork?" Stiles asked, without looking up from his reading.
Derek considered for a moment. "Maybe. There's some musical instruments in the Vault. Why?"
"This purification rite calls for a specific tone at the end," Stiles pointed to the section of the book he had been studying. "For lack of a better term, it 'seals' the rite."
"Why a tuning fork?" Derek asked.
"Seemed the simplest," Stiles shrugged. I don't have perfect pitch and I need something to help me generate the proper note."
"You mean there's actually something you can't look up on Wikipedia?" Derek teased.
"Hey! I actually tried that!" Stiles replied. "The tones on the computer speakers aren't clean enough for what I need. And if we don't do this right, that would be worse that not doing it at all."
"I guess that makes sense," Derek agreed.
"So. The Vault?" Stiles prompted.
"I remember Great-Aunt Olivia talking about some musical instruments a few times, is all," Derek admitted. "I think she played a guitar or something stringed. But anything there would have been mothballed. I don't know how useful they will be."
"I need something already in tune," Stiles frowned. "I don't have time to mess with trying to get something into tune."
"Then we call a music shop," Derek said patiently. "There's a couple of good shops in town. We can call them in the morning, and they can help us with what you need."
Stiles leaned in for a soft kiss. "I knew I kept you around for a good reason!"