Joan Watson

"I have an acquaintance in New York City's bioterrorism squad," Sherlock says as they leave the brownstone and stride toward the nearest cross street to hail a cab. "He is, in addition to being one of the premiere analysts in his field, something of a collector when it comes to molds. I grew a rare toxic mold sample for him. Both very difficult and very illegal. He owes me a rather large favor for that."