"Sherlock!" Molly Hooper raised her voice. She had been standing behind the consulting detective for at least five minutes and he was steadfastly ignoring her. Out of exasperation, she unplugged the microscope into which he was intently peering.
"Molly, I am in the middle of examine this woman's blood." Sherlock reached down to turn the instrument back on, only to find a petite hand covering the switch. He finally looked up, unconsciously turning a pair of large puppy eyes towards the pathologist.
She blinked, caught off-guard by Sherlock's expression. "It, it's not in the blood." Molly told him briskly, turning back to the body of recently-deceased Andrea McKellan.
It's not in the blood. Sherlock began rearranging the case room in his mind palace. "Of course," he breathed. "It's completely obvious. It was in her stomach. The suspect takes her out for lunch, on the pretense of…" His eyes scanned the body once more. Library card. Unrelated. Drugs? Molly would have mentioned that; it would be present in a blood sample, anyway.
"Not a bad deduction," Sherlock looked up to see the pathologist smirking at him. "Entirely incorrect, I'm afraid. Anaphylactic shock. I'm certain you saw the cells were sick…" Molly trailed off, uncertain of the detective's expression.
Sherlock nodded, busy in his mind palace, piecing Molly's story together.
"Not poisoned. Just sick. But when a person goes into anaphylactic shock, their body has no time. They need antihistamines immediately. This may have been deliberate, but it wasn't poison." She concluded, looking up to see Sherlock already calling the DI, telling him that the case had been solved and that he was already hailing a cab from St. Bart's. Molly's eyes followed him as he disappeared, a faint half-smile fading from her face. "Thanks, Molly," she muttered as she began preparing the body.