High above Edo Castle, the keep’s gloomy top story echoed with the footsteps of guards patrolling the corridors and stairways below. Afternoon sunlight filtered through the barred windows to hang in thin, dusty shafts in the air. Chamberlain Yanagisawa stood facing a window, his tall, elegant form silhouetted against the alternating bands of light and dark.

“So, kunoichi,” he said. A sneer curled the edges of his voice. “What information have you and your spy network managed to collect regarding Sōsakan Sano?”

Aoi, standing behind him, flinched at the way he’d addressed her. Kunoichi: female ninja; practitioner of the dark martial arts, descended, as legend claimed, from demons with supernatural powers. She didn’t object to the term; she was proud of what she was. But Yanagisawa’s open contempt started a slow, angry fire in her blood. Deeper than that of a man for a woman, superior for inferior, it echoed that in which the samurai had held the ninja since time immemorial. They despised her people as dirty mercenaries who used stealth, sabotage, covert assassination, espionage, and deception instead of the forthright samurai martial arts. Aoi wondered whether Chamberlain Yanagisawa realized that his class had created the demons themselves. Once peace-loving Buddhist mystics, the ninja had developed their famed, deadly skills as a defense against the ruling samurai who burned the temples and killed the worshippers in an attempt to destroy what they didn’t understand. However, this aversion had never stopped Yanagisawa and his kind from employing the ninja to do work that they themselves considered dishonorable, cowardly, and beneath them.

Like using her to spy on a helpless subordinate.

Swallowing her own contempt for her master, Aoi said, “Sano rises early to practice the martial arts every day. He works long hours in the archives. He eats and drinks moderately.” Rigorous training enabled her to purge her voice of all emotion as she related the information reported to her by Sano’s servants. “He never goes to the Yoshiwara pleasure quarter, but does visit his old mother. He doesn’t gamble, or squander money on trifles. When he attends parties, he always returns home early to sleep alone.”

While she spoke, Aoi pictured herself standing at the end of a long line of ninja that began more than two hundred years ago and spanned the long wars that had preceded the Tokugawa regime. She saw Fumo Kotarō, who had aided Lord Hōjō Odawara though secret night attacks on the enemy Takeda; Saiga Magoichi, master of firearms and explosives; and the Hattori ninja, who had established the metsuke and served as chief of security at Edo Castle. And always behind the scenes, the women, shadowy figures whose names did not appear in any historical account. Disguised as servants, prostitutes, entertainers-or shrine attendants like herself-they’d acted as spies and assassins, compromising the enemy in ways that male agents couldn’t.

But now the wars were over. Most surviving ninja had returned to their secret mountain villages. Some had become criminals or private security guards in the cities. The line of ninja who aided the ruling warrior class in their military and political schemes ended with her. She was an anachronism, serving the Tokugawa under the same threat used against her ancestors: annihilation of their kind. If she refused to obey, the Tokugawa would kill her, then send troops into the mountains to destroy her clan and the other families that comprised their small ninja school. It had happened before; it could happen again. In Japan, families were routinely punished for a member’s offenses. Aoi fought her impotent rage, reminding herself that negative emotions are sources of strength, but only if used properly.

“Sano doesn’t have a mistress, or force himself on the maids or stableboys,” she finished. “From what my informers tell me, he’s exactly what he seems: A man focused entirely on his duties. A perfect samurai.”

Unlike Yanagisawa, who possessed all the vices and weaknesses that Sano did not. What a despicable creature!

Yanagisawa’s silk robes hissed and slithered against the floor as he turned to face her. The bright window backlit him, leaving his face shaded, but Aoi, with her keen vision, saw the anger that rendered his handsome features ugly.

“ ‘A perfect samurai.’ ” His mocking repetition issued from between clenched teeth.

Aoi’s sharp senses detected the slight turbulence in the air around him, and the faint bitter scent that his body exuded. Both betrayed his overweening fear and hatred of Sano. Focusing her trained concentration upon Yanagisawa, she probed for the reason he would waste such strong emotions and relentless effort on an underling. He had a reputation for ruining early the careers of men who might eventually rise to compete with him for status and power. And Sano, by virtue of having saved the shogun’s life, was in a unique position to do so. But Yanagisawa’s next words distracted her, masking his motives.

“Two months of surveillance, with nothing to show for it but proof of Sano’s good character!” He began to pace the corridor in swift, restless strides. “And now that His Excellency has appointed him to investigate Kaibara Tōju’s murder, it is more important than ever to find a weapon to use against him.”

Yanagisawa halted in midstep before her. “Are you sure the virtuous Sano has no weaknesses that can be exploited?”

Aoi felt a growing sympathy toward Sano, perhaps because of her hatred for this man who schemed against him; perhaps because Sano’s quiet intelligence and modesty made him so different from the typical brutish, egotistical samurai. This sympathy frightened her. She must not let her personal feelings interfere with her mission when so much lay at stake. But just for a moment she envisioned Sano’s face, with its thoughtful, wary expression. She remembered the physical attraction she’d felt toward him- which she knew he shared. He was a man she might have liked, under different circumstances…

She dismissed the idle fantasy and said, “He’s lonely. And loneliness makes people vulnerable.”

How well she knew loneliness. As Yanagisawa continued to rant about Sano, the surface of her trained mind captured his words and committed them to memory. On another, deeper level, she relived her life, starting with the day she’d left her native Iga Province.

She saw herself on that misty autumn day fifteen years ago, at age fourteen, a student at the secret academy in the mountains where young kunoichi learned combat and espionage skills. She was running a woodland obstacle course of trees, rocks, horizontal poles, and inclined planks, in an exercise designed to incorporate speed, balance, agility, and silence into her body’s movements. At the end stood her beloved father: the powerful jōnin-high man-of the Iga ninja school. His tragic expression froze her.

“Father, what’s wrong?” she asked.

“Aoi, the time has come for you to begin the work you’ve been trained for,” he said sadly. “Today you leave for Edo Castle, to become an apprentice spy.”

Aoi hugged herself, buffeted by a desolation as cold as the mountain wind. Her inevitable departure had always belonged to the distant future. But now the future was here.

Her father’s eyes reflected her anguish, but he said only, “It is necessary.”

Trained in ninjutsu since early childhood, Aoi knew better than to ask why. A jōnin made all the clan’s decisions, based on his superior knowledge of the scheme of totality, and lower members must accept them without challenge. But she’d guessed that the ninja, to ensure their own survival, would always serve whoever stood the best chance of gaining and keeping power. And her father was betting on the Tokugawa. That he would send them his best and dearest young kunoichi proved it. Aoi wanted to weep and rage and refuse, but her training forbade her to do anything but say, “Yes, Father. I’ll go and get ready.”