Simon’s heart went cold.

He had quite literally caught the Thief of Mayfair in his arms—and the two-faced criminal was none other than headmistress Dahlia Grenville.

Ex-headmistress.

He dropped her unceremoniously onto the expensive, high society carpet.

As she fell, a palm-sized leather-bound book had popped out of her bodice, along with a scrap of lace apparently meant to keep both bosoms and contraband safely out of sight.

He nudged the expensive leather volume with the toe of his boot.

She winced and covered her eyes.

Simon did not. His were finally open. And he could not have felt more betrayed.

Dahlia was not who he’d thought she was. He’d been shocked to glimpse her hobnobbing with aristocrats. Not waiting on them as a servant, or even rubbing shoulders on accident, going about the duties of an honest, hardworking boarding school administrator.

No, she’d been swanning about in a gown so exquisite it hurt the eyes. Laughing with this duchess or that countess as if they were old friends. Because they were.

She had never been part of Simon’s world. She’d been born into another plane. One of champagne and hors d'œuvres, diamonds and pearls, lady’s maids and liverymen whose daily uniforms cost more than Simon’s annual salary. Dahlia was far from the hard-luck, working-class angel he’d believed her to be.

She was a liar. A hypocrite. A beautiful, mercenary, Janus-faced thief.

He’d never known her at all.

“Get up,” he growled.

She leapt to her feet with the agility of an acrobat. Or the grace of a debutante with a private dancing-master and expensive finishing school.

Or the habits of a well-practiced thief.

“Why are you here?” she stammered, with a glance over her shoulder. “Did you follow me?”

“I was hunting the Thief of Mayfair,” he said coldly. “So, yes. It appears I followed you.”

Her cheeks flushed. “But how did you know I’d be here?”

“I didn’t have to,” he said simply. “The Thief of Mayfair targets wealthy aristocrats, either during or shortly after a showy gathering. Once I compiled a list of upcoming ton parties, it was easy to determine which hosts had items of great value within easy reach. Those individuals tend to share that information with the entire world.”

Dahlia lowered her head. “Lady Pettibone paid you to guard her library?”

“That would be unethical.” Simon flashed a hard smile. “The government already pays me to investigate crimes and protect its citizens. What kind of monster would I be to accept money I didn’t deserve?”

She swallowed visibly. “Simon, I—”

“No need to explain,” he said icily. “I know what you are. I observed you in your natural environment.”

“You…saw me with the other ladies?” she guessed hopefully.

“Believe me. Your ratafia consumption is the least of my concerns.” Stuffing expensive objects into her bodice was quite another. There was no denying the evidence.

Dahlia was a thief.

His heart hardened as he plucked the fallen book from the ground.

“It isn’t mine,” she blurted.

He slid her a flat look. “Obviously.”

“That doesn’t mean I was stealing it,” she said quickly. But her face had drained of color.

“Doesn’t it?” he said in bored tones.

“Or that I’m the Thief of Mayfair,” she added.

“Aren’t you?”

“I…” She rolled back her shoulders. “I was forced to lie down in the guest quarters due to a megrim.”

“Ill-timed, I’m sure,” he murmured.

“Ask the maids,” she insisted. “They saw me. When I had recovered enough to return to the party, I passed through the library and simply lost track of time.”

“For two hours.” He didn’t bother to hide his skepticism.

“It’s…a good library,” she mumbled.

“It’s off limits,” he corrected firmly. “Lady Pettibone told you so personally.”

Dahlia cringed. “You heard her say that?”

“She tells everyone. Lying to me doesn’t change facts.” He held up the book. “You broke in to steal from her.”

“I didn’t break in,” Dahlia hedged.

“But you do steal. You’ve done so all season.” He curled his lip. “The signs were there. I just didn’t want to see them.”

She winced. “There were signs I was a thief?”

“Signs you were an…unusual headmistress,” he allowed. “I thought it was charming at first.”

“Did you?” She raised her lashes to stare at him.

It no longer mattered. He crossed his arms. “If I search the school, will I find the stolen objects?”

“Only if you look in the schoolroom.” She leaned forward in defiance. “Pocket globes and a trio of disintegrating reading primers are the sum total of our educational materials.”

“That doesn’t make stealing right.”

“Does it make it wrong?” Her gaze turned pleading. “All the objects were returned to their rightful owners.”

“Except the pocket globes,” he pointed out.

“Mapleton’s a special case,” she muttered. “I’m half-surprised one of his competition hasn’t stomped on his collection long ago.”

Frankly, so was Simon. The man was a slug. But it didn’t change facts.

He hardened his voice toward Dahlia. “You have to give them back.”

And he had to turn her in.

She sent another furtive glance over her shoulder. “Where is everyone? Aren’t you going to parade me in front of Lady Pettibone?”

“I shall parade you inside the Magistrates’ Court,” he promised. “Lady Pettibone took her post-party laudanum, and there is no need to wake her.”

Hope entered Dahlia’s eyes for the first time since she’d fallen into his arms. “So, right now…nobody knows but us?”

Simon raised a brow.

He knew what she was asking. As things stood, they could both walk away. No one would know…but Simon. Except it was his job to ensure such travesties of justice never happened.

No. More than that. It was Simon’s mission. The driving force that had given his life meaning ever since his parents’ death at the hands of a highwayman. A highwayman who had never been caught.

But what if he had? What if months or weeks earlier, some soft-hearted imbecile had agreed to give the blackguard a second chance? That was somehow worse than Simon’s long held belief that the highwayman had simply managed to evade capture.

One lazy watchman, one corrupt magistrate, one irresponsible investigator was all it took to put others’ lives and property at risk. Simon had sworn never to be one of them. Had held his head high for three ethical decades that would make any man proud. But he hadn’t done it for himself, or even to avenge the death of his mother. He did it because it was the right thing to do. All people deserved to be treated fairly. By their contemporaries—and in the eyes of the law.

Which meant there was no choice here. Not for him, and not for Dahlia. A thief was a thief. And crime had to pay.

Even if it meant sending the love of his life to Newgate.

He tried to swallow the ball of anger and betrayal clogging his throat.

To say he was disappointed in her would be a laughable understatement. He’d believed in her goodness. Wanted to marry her, for the love of God. Had possessed absolute, wholehearted faith that she was precisely the sort of woman that would make any Bow Street inspector proud.

And everything about her was a lie.

Until recently, he’d believed all his dreams would come true if only he could earn a coveted promotion by catching the Thief of Mayfair. Turned out, the villain was his would-be fiancée. Whose big brown eyes were glassy with unshed tears because the man she’d refused to marry was the only one who could save her from the gallows.

It was no longer about his career, or his promotion. Turning her in meant ruining her life. Even prisoners who weren’t sentenced to hang never lasted long in the squalid, disease-filled prisons.

Yet he’d sworn an oath to do the right thing, even when it was hard. Especially when it was hard. The hardest thing he’d ever have to do in his life.

“Simon?” she said, her eyes and voice pleading.

He pulled out his iron handcuffs and snapped them onto her wrists.