"Harry!" Hermione said brightly, as he caught her eye. She pulled him into a kiss, and then introduced him to their fellow secret agent.
"This is Dr. Wembley," she said. "He's the chemist that's been examining the oil samples that we collected from the firth."
"Nice to meet you," said Harry, as he shook the muggle's hand. "I assume that you discovered something of interest, since my girlfriend looks like she's about to pee her pants."
"Harry!" Hermione chided, as she slapped his shoulder.
"That might actually help confirm my hypothesis," the chemist said with a sardonic grin. "Being that urine is also fluorescent."
Hermione snapped her head back towards the chemist, but then grinned and nodded her head. "You are rather clever, aren't you?"
"Will someone explain this cleverness to an ignorant wizard?" asked Harry.
The Q Branch chemist turned towards Harry and smiled. "The two crude oil samples were chemically identical, but then I considered their physical properties."
"One was orange and one wasn't when we collected them," noted Harry.
"But when we submitted them to the lab they were both black, remember?" asked Hermione.
"So how does this relate to your pee?" asked Harry.
Hermione shook her head dismissively. "Both crude oil and urine, I presume, fluoresce, or glow in the dark, when exposed to ultraviolet radiation."
Harry squinted at Hermione, then turned to their colleague for confirmation.
"Except that urine fluoresces purple," the chemist said with a smirk. He then added, "But I digress…once I thought to check it was a simple matter to verify in the laboratory."
"You examined your pee in your laboratory?" asked Harry.
"No, Major Potter, the crude oil samples," the chemist replied. "Both of them glowed orange when exposed to short-wavelength ultraviolet radiation."
Harry paused, waiting for something more. When nothing came, he asked, "And so…"
"And so, Harry, your Patronus may have produced the same glow because it is comprised, at least in part, of short-wave ultraviolet light."
Harry nodded. "And so….."
"Oh, Harry," Hermione said with a sigh. "Muggles can't cast Patronus charms, but they can create ultraviolet light."
"So you think that the ultraviolet radiation is the secret ingredient within a Patronus that scares off the Dementors?"
Hermione nodded and shrugged her shoulders. "We'd have to test the idea, of course, but just think if that's the case!"