Hirata stepped around trampled scrolls, to an area of floor that was bare amid the mess. There, large, reddish-brown stains soiled the tatami. “It’s blood,” Hirata said.

“And that area of bare floor is roughly the size of a human body,” Sano said.

“Makino could have been murdered here and moved to his bed afterward,” Hirata said eagerly. “If so, then maybe his death wasn’t just a simple love crime.”

Sano replied in a neutral tone, “Let’s not jump to conclusions.”

But hope sparked Hirata’s detective instincts. He stepped over to the window near the desk and slid aside the wooden grid of paper panes. Behind it were plank shutters. An iron catch that had secured them dangled loose.

“This window has been forced.” Hirata touched the splintered wood on the shutters, where a blade or other hard, flat object inserted between them had torn away the catch.

Sano joined him and inspected the window. “So it has.”

He pushed open the shutters and revealed a small garden courtyard. A patch of grass, bordered by raked white sand, contained a flagstone path, a pond, and a stone lantern. Hirata and Sano peered at the evergreen shrub beneath the window.

“Trampled branches,” Hirata said.

“And footprints in the sand,” Sano said, pointing.

“It looks as though an intruder broke into the study and attacked Makino,” Hirata said. “There was a violent struggle. The intruder killed Makino, then put him to bed as if he’d died there. Afterward, the intruder escaped.” Hirata anticipated a hunt for the assassin, during which he triumphantly restored himself to Sano’s good graces. “The evidence says so.”

“The other evidence suggests a crime of passion,” Sano countered. “Both theories can’t be true.”

Hirata could think of arguments in favor of the theory he preferred, but although he once would have felt free to debate with Sano, their bad blood now threatened to turn every discussion into a quarrel. “You’re right,” he said. “The evidence is too contradictory for us to be sure what happened.”

“I’ll see if Makino himself can tell us how he died,” Sano said, and Hirata knew he meant he was going to Edo Morgue to examine the corpse. “While I’m gone, you interview everyone in the estate. Find out where they were last night. Also look for more signs that an assassin broke into the estate.”

“Yes, Sōsakan-sama.” Hirata had capably performed inquiries like this many times; but did Sano now doubt that he would do as told?

Sano said, “For now, we’ll proceed under the assumption that Makino was murdered, and everyone inside the estate is a suspect. So are all of Makino’s enemies outside.”

Hirata recognized the wide scope of the case, but his spirit leaped at the challenge.

“The shogun must be informed about Makino’s death and the investigation,” Sano said. “I’ll request an audience with him this evening.”

As he and Sano parted, Hirata made a vow to learn as much as possible before they reported to the shogun. And by the end of the investigation, he would redeem himself as Sano’s loyal chief retainer and an honorable samurai.

A bleak, sunless afternoon cast a pall over Kodemma-cho, the slum in the northeast sector of the Nihonbashi merchant district. Miserable shacks lined the twisting roads, along which filthy beggars warmed themselves at bonfires. Stray dogs and ragged, noisy children scavenged amid garbage heaps. Dispirited laborers, peddlers, and housewives plodded along open gutters streaming with foul water. They paid no attention to the samurai dressed in patched, threadbare garments who rode a decrepit horse through their midst.

Sano, disguised as a rōnin, kept his hat tipped low over his face as he headed toward Edo Jail, which raised its high walls and gabled roofs in the distance. Crossing the rickety bridge over the canal that fronted the prison, he paused, wary of spies. As his prominence in the bakufu had grown, so had his need for secrecy. No one must know that the shogun’s sōsakan-sama frequented this place of death and defilement. And no one must associate this visit with his investigation into the murder of Senior Elder Makino.

The two guards stationed outside the jail opened the heavy, iron-banded gate for Sano. They knew who he was, but he paid them a salary to ignore his business and tell no tales. Once he’d ridden through the portals, Sano bypassed the fortified dungeon from which prisoners’ howls emanated. He dismounted outside Edo Morgue, a low structure with scabrous plaster walls, a shaggy thatched roof, and barred windows.

Through the door emerged Dr. Ito Genboku, morgue custodian, followed by Detectives Marume and Fukida. The doctor wore a dark blue coat, the traditional garb of the medical profession; the wind ruffled his white hair. He and Sano had met five years ago, while Sano was a police commander investigating his first murder case, and had become friends.

“Good afternoon, Ito-san,” Sano said, bowing. “I see that my detectives have arrived with the body I sent.”

Dr. Ito returned the bow and greeting. “I was amazed when they told me who it was. I’ve never examined the corpse of such an important person.” Concern deepened the lines in Dr. Ito’s ascetic face. “You took a big risk sending it here.”

“I know.” If Sano’s colleagues in the bakufu learned of his actions, there would be a scandal and he would be condemned for defiling Makino as well as for breaking the law against foreign science. Before him stood an example of what could happen.

Dr. Ito, once a prominent physician, had performed medical experiments and obtained scientific knowledge from Dutch traders. While the usual punishment for such offenses was exile, the bakufu had consigned Dr. Ito to a life sentence as custodian of Edo Morgue. Here he could continue his scientific studies in peace, but he’d lost his family, his status, and his freedom.

“We didn’t bring Makino straight from his house to the jail,” Detective Fukida said. “We brought him home first, removed him from the trunk, and put him in a palanquin, in a compartment under the floorboards.”

“Then we rode out of Edo Castle in the palanquin,” Detective Marume added. “The checkpoint guards never suspected there was anyone in it except us.”

“No one followed me, either,” Sano said.

Dr. Ito smiled wryly. “Your subterfuges are most ingenious. I recall that the last body you sent was hidden in a crate of vegetables. You’ve been lucky so far.”

“Well, we’d better examine Makino while my luck holds,” Sano said. “I have to get his body home before its absence raises any questions.”

“I am ready to begin.” Dr. Ito ushered Sano and the detectives into the morgue.

Its single large room was furnished with stone troughs used for washing the dead, cabinets containing tools, a podium stacked with papers, and three high tables. One table held a prone figure shrouded with a white drape. Beside it stood Dr. Ito’s assistant, Mura. In his late fifties, Mura had hair gradually turning from gray to silver and a square face with a somber, intelligent aspect.

“Proceed, Mura-san,” Dr. Ito said.

Everyone gathered around the table, and Mura folded back the drape. He was an eta-a member of Japan ’s outcast class, whose hereditary link with death-related occupations such as butchering and tanning rendered them spiritually contaminated. Other citizens shunned them. They served Edo Jail as wardens, corpse handlers, torturers, and executioners. Mura, befriended and educated by Dr. Ito in defiance of class customs, performed all the physical work associated with his master’s studies. Now Mura and everyone else beheld Senior Elder Makino. He lay clothed in his nightcap and beige robe, his hands still on his chest, his thin ankles protruding. His knobby feet, shod in white socks, pointed at the ceiling. Permanent slumber shadowed his skull-like face.