She never gave the appearance of hurrying, but covered an immense amount of ground during the day, pacing the flat gray stones of the Hopital wards with a stride that covered a yard at a time, her small white dog Bouton hurrying at her heels to keep up.

A far cry from the fluffy lapdogs so popular with the ladies of the Court, he looked vaguely like a cross between a poodle and a dachshund, with a rough, kinky coat whose fringes fluttered along the edges of a wide belly and stumpy, bowed legs. His feet, splay-toed and black-nailed, clicked frantically over the stones of the floor as he trotted after Mother Hildegarde, pointed muzzle almost touching the sweeping black folds of her habit.

“Is that a dog?” I had asked one of the orderlies in amazement, when I first beheld Bouton, passing through the Hopital at the heels of his mistress.

He paused in his floor-sweeping to look after the curly, plumed tail, disappearing into the next ward.

“Well,” he said doubtfully, “Mother Hildegarde says he’s a dog. I wouldn’t like to be the one to say he isn’t.”

As I became more friendly with the nuns, orderlies, and visiting physicians of the Hopital, I heard various other opinions of Bouton, ranging from the tolerant to the superstitious. No one knew quite where Mother Hildegarde had got him, nor why. He had been a member of the Hopital staff for several years, with a rank – in Mother Hildegarde’s opinion, which was the only one that counted – well above that of the nursing sisters, and equal to that of most of the visiting physicians and apothecaries.

Some of the latter regarded him with suspicious aversion, others with jocular affability. One chirurgeon referred to him routinely – out of Mother’s hearing – as “that revolting rat,” another as “the smelly rabbit,” and one small, tubby truss-maker greeted him quite openly as “Monsieur le Dishcloth.” The nuns considered him something between a mascot and a totem, while the junior priest from the cathedral next door, who had been bitten in the leg when he came to administer the sacraments to the patients, confided to me his own opinion that Bouton was one of the lesser demons, disguised as a dog for his own fell purposes.

In spite of the unflattering tone of the priest’s remarks, I thought that he had perhaps come the closest to the truth. For after several weeks of observing the pair, I had come to the conclusion that Bouton was in fact Mother Hildegarde’s familiar.

She spoke to him often, not in the tone one generally uses for dogs, but as one discussing important matters with an equal. As she paused beside this bed or that, often Bouton would spring onto the mattress, nuzzling and sniffing at the startled patient. He would sit down, often on the patient’s legs, bark once, and glance up inquiringly at Mother, wagging his silky plumed tail as though asking her opinion of his diagnosis – which she always gave.

Though I was rather curious about this behavior, I had had no opportunity of closely observing the odd pair at work until one dark, rainy morning in March. I was standing by the bed of a middle-aged carter, making casual conversation with him while I tried to figure out what in bloody hell was wrong with the man.

It was a case that had come in the week before. He had had his lower leg caught in the wheel of a cart when he carelessly dismounted before the vehicle had stopped moving. It was a compound fracture, but a fairly uncomplicated one. I had reset the bone, and the wound seemed to be healing nicely. The tissue was a healthy pink, with good granulation, no bad smell, no telltale red streaks, no extreme tenderness, nothing at all to explain why the man still smoldered with fever and produced the dark, odorous urine of a lingering infection.

“Bonjour, Madame.” The deep, rich voice spoke above me, and I glanced up at the towering form of Mother Hildegarde. There was a whish past my elbow, and Bouton landed on the mattress with a thump that made the patient groan slightly.

“What do you think?” said Mother Hildegarde. I wasn’t at all sure whether she was addressing me or Bouton, but took the benefit of the doubt and explained my observations.

“So, there must be a secondary source of infection,” I concluded, “but I can’t find it. I’m wondering now whether perhaps he has an internal infection that’s not related to the leg wound. A mild appendicitis, or a bladder infection, perhaps, though I don’t find any abdominal tenderness, either.”

Mother Hildegarde nodded. “A possibility, certainly. Bouton!” The dog cocked his head toward his mistress, who jerked an oblong chin in the direction of the patient. “A la bouche, Bouton,” she ordered. With a mincing step, the dog pushed the round black nose that presumably gave him his name into the carter’s face. The man’s eyes, heavy-lidded with fever, sprang open at this intrusion, but a glance at the imposing presence of Mother Hildegarde stopped whatever complaint he might have been forming.

“Open your mouth,” Mother Hildegarde instructed, and such was her force of character that he did so, even though his lips twitched at the nearness of Bouton’s. Dog-kissing plainly wasn’t on his agenda of desirable activities.

“No,” said Mother Hildegarde thoughtfully, watching Bouton. “That isn’t it. Have a look elsewhere, Bouton, but carefully. The man has a broken leg, remember.”

As though he had in fact understood every word, the dog began to sniff curiously at the patient, nosing into his armpits, putting stubby feet on his chest in order to investigate, nudging gently along the crease of the groin. When it came to the injured leg, he stepped carefully over the limb before putting his nose to the surface of the bandages round it.

He returned to the groin area – well, what else, I thought impatiently, he’s a dog, after all – nudged at the top of the thigh, then sat down and barked once, wagging triumphantly.

“There it is,” said Mother Hildegarde, pointing to a small brown scab just below the inguinal crease.

“But that’s almost healed,” I protested. “It isn’t infected.”

“No?” The tall nun placed a hand on the man’s thigh and pressed hard. Her muscular fingers dented the pale, clammy flesh, and the carter screamed like a banshee.

“Ah,” she said in satisfaction, observing the deep prints left by her touch. “A pocket of putrefaction.”

It was; the scab had loosened at one edge, and a thick ooze of yellow pus showed under it. A little probing, with Mother Hildegarde holding the man by leg and shoulder, revealed the problem. A long sliver of wood, flying free of the splintered cartwheel, had driven upward, deep into the thigh. Disregarded because of the apparently insignificant entrance wound, it had gone unnoticed by the patient himself, to whom the whole leg was one giant pain. While the tiny entrance wound had healed cleanly, the deeper wound had festered and formed a pocket of pus around the intrusion, buried in the muscle tissue where no surface symptoms were visible – to human senses, at least.

A little scalpel work to enlarge the entrance wound, a quick grip with a pair of long-nosed forceps, a smooth, forceful pull – and I held up a three-inch sliver of wood, coated with blood and slime.

“Not bad, Bouton,” I said, with a nod of acknowledgment. A long pink tongue lolled happily, and the black nostrils sniffed in my direction.

“Yes, she’s a good one,” said Mother Hildegarde, and this time there was no doubt which of us she was speaking to, Bouton being male. Bouton leaned forward and sniffed politely at my hand, then licked my knuckles once in reciprocal acknowledgment of a fellow professional. I repressed the urge to wipe my hand on my gown.

“Amazing,” I said, meaning it.

“Yes,” said Mother Hildegarde, casually, but with an unmistakable note of pride. “He’s very good at locating tumors beneath the skin, as well. And while I cannot always tell what he finds in the odors of breath and urine, he has a certain tone of bark that indicates unmistakably the presence of a derangement of the stomach.”