He grinned at her, slowly, showing his teeth, but his eyes remained cold. “What do you think you’re doing?”

“That’s the man over there, and any minute Duke and Charles will arrive. I’m giving us a perfectly reasonable reason for following the man when he leaves, together.”

His lips remained curved; he slid one arm about her waist and pulled her closer, bending his head to whisper in her ear, “You are not coming with me.”

She smiled into his eyes, patted his chest. “Unless the man goes into the stews, and that hardly seems likely, I am.”

He narrowed his eyes at her; she smiled more brightly, but met his gaze directly. “I’ve been a part of this drama from the beginning. I think I should be a part of its end.”

The words gave Tristan pause. And then fate stepped in and took the decision from him.

The bell towers of London’s churches tolled the hour—three clangs, echoed and repeated in multiple keys—and Duke came striding swiftly along the pavement and turned in at Queen Anne’s Gate.

Charles, in the guise of a tavern brawler, came sauntering along a little way behind, timing his approach.

Duke halted, saw his man, and marched toward him. He looked neither right nor left; Tristan suspected Charles had drilled him until he was so focused on what he had to do, so desperate to get it right, that paying attention to anything else was presently beyond him.

The wind was in the right quarter; it wafted Duke’s words to them.

“Do you have my vowels?”

The demand took the foreigner aback, but he recovered swiftly. “I might have. Have you got the formula?”

“I know where it is, and can get it for you in less than a minute, if you have my vowels to give me in return.”

Through narrowing eyes, the foreign gentleman searched Duke’s pale face, then he shrugged, and reached into his coat pocket.

Tristan tensed, saw Charles lengthen his stride; they both relaxed a fraction when the man drew out a small packet of papers.

He held them up for Duke to see. “Now,” he said, his voice cold and crisply accented, “the formula, if you please.”

Charles, until then apparently about to stroll past, changed direction and with one step joined the pair. “I have it here.”

The foreigner started. Charles grinned, wholly evil. “Don’t mind me—I’m just here to make sure my friend Mr. Martinbury comes to no harm. So”—he nodded at the papers, glanced at Duke—“they all there then?”

Duke reached for the vowels.

The foreigner drew them back. “The formula?”

With a sigh, Charles pulled out the copy of the altered formula Humphrey and Jeremy had prepared and made to look suitably aged. He unfolded it, held it up where the foreigner could see it but not quite read it. “Why don’t I just hold it here, then as soon as Martinbury has checked over his vowels, you can have it.”

The foreigner was clearly unhappy, but had little choice; Charles was intimidating enough in civilized garb—in his present guise, he exuded aggression.

Duke took the vowels, quickly checked, then looked at Charles and nodded. “Yes.” His voice was weak. “They’re all here.”

“Right then.” With a nasty grin, Charles handed the formula to the foreigner.

He seized it, pored over it. “This is the right formula?”

“That’s what you wanted—that’s what you’ve got. Now,” Charles continued, “if you’re done, my friend and I have other business to see to.”

He saluted the foreigner, a parody of a gesture; taking Duke’s arm, he turned. They marched straight out of the gate. Charles hailed a hackney, bundled a now trembling Duke in, and climbed in after him.

Tristan watched the carriage rumble off. The foreigner looked up, watched it go, then carefully, almost reverently, folded the formula and slipped it into his inner coat pocket. That done, he adjusted his grip on his cane, straightened his back, pivoted on his heel, and walked stiffly back toward the lake.

“Come on.” His arm around Leonora, Tristan straightened away from the tree and started off in the man’s wake.

They passed Humphrey; he didn’t look up but Tristan saw that he’d produced a sketch pad and pencil and was rapidly drawing, a somewhat incongruous sight.

The foreigner didn’t look back; he seemed to have swallowed their little charade. They’d hoped he would head straight back to his office rather than into any of the less salubrious areas not far from the park. The direction he was taking looked promising. Most of the foreign embassies were located in the area north of St. James’s Park, in the vicinity of St. James’s Palace.

Tristan released Leonora, then took her hand, glanced down at her. “We’re out for a night of entertainment—we’ve decided to look in at one of the halls around Piccadilly.”

She opened her eyes wide. “I’ve never been to one—I take it I should treat the prospect with enthusiam?”

“Precisely.” He couldn’t help but grin at her delight—nothing to do with any music hall but the result of pure excitement.

They passed Deverell, who’d got to his feet and was brushing himself down preparatory to joining them in following their quarry.

Tristan was an expert at trailing people through cities and crowds; so, too, was Deverell. They’d both worked primarily in the larger French cities; the best methods of the chase were second nature.

Jeremy would collect Humphrey and they’d return to Montrose Place to await developments; Charles would be there ahead of them with Duke. It was Charles’s job to hold the fort until they returned with the last, vital piece of information.

Their quarry crossed the bridge over the lake and continued on toward the environs of St. James’s Palace.

“Follow my lead in all things,” Tristan murmured, his eyes on the man’s back.

Just as he’d expected, the man paused just before the gate leading out of the park and bent down as if to ease a stone from his shoe.

Sliding his arm around Leonora, Tristan tickled her; she giggled, squirmed. Laughing, he settled her familiarly against him, and continued straight past the man without so much as a look.

Breathless, Leonora leaned close as they continued on. “Was he checking?”

“Yes. We’ll stop a little way along and argue about which way to go so he can pass us again.”

They did; Leonora thought they put on a creditable performance of a pair of lower-class lovers debating the merits of music halls.

When the man was once more ahead of them, striding along, Tristan grasped her hand, and they followed, now rather more briskly as if they’d made up their minds.

The area surrounding St. James’s Palace was riddled with tiny lanes and interconnecting alleyways and yards. The man turned into the labyrinth, striding along confidently.

“This won’t work. Let’s leave him to Deverell and go on to Pall Mall. We’ll pick him up there.”

Leonora felt a certain wrench as they left the man’s trail, continuing straight on where he had turned left. A few houses along, she glanced back, and saw Deverell turn off in the man’s wake.

They reached Pall Mall and turned left, ambling very slowly, scanning the openings of the lanes ahead. They didn’t have long to wait before their quarry emerged, striding along even more quickly.

“He’s in a hurry.”

“He’s excited,” she said, and felt certain it was true.

“Perhaps.”

Tristan led her on; they switched with Deverell again in the streets south of Piccadilly, then joined the crowds enjoying an evening stroll along that major thoroughfare.

“This is where we might lose him. Keep your eyes peeled.”

She did, scanning the throng bustling along in the fine evening.

“There’s Deverell.” Tristan stopped, nudged her so she looked in the right direction. Deverell had just stepped into Pall Mall; he was looking about him. “Damn!” Tristan straightened. “We’ve lost him.” He started openly searching the crowds before them. “Where the devil did he go?”

Leonora stepped closer to the buildings, looked along the narrow gap the crowds left. She caught a flash of grey, then it was gone.

“There!” She grabbed Tristan’s arm, pointed ahead. “Two streets up.”

They pushed through, tacked, ran—reached the corner and rounded it, then slowed.

Their quarry—she hadn’t been wrong—was almost at the end of the short street.

They hurried along, then the man turned right and disappeared from view. Tristan signaled to Deverell, who started running along the street after the man. “Down the alley.” Tristan pushed her toward the mouth of a narrow lane.

It cut straight across to the next street running parallel to the one they’d been on. They hurried along it, Tristan gripping her hand, steadying her when she slipped.

They reached the other street and turned up it, strolling once more, catching their breaths. The opening where the street the man had turned down joined the one they were now on lay ahead to their left; they watched it as they walked, waiting for him to reappear.

He didn’t.

They reached the corner and looked down the short street. Deverell stood leaning against a railing at the other end.

Of the man they’d been following there was absolutely no sign.

Deverell pushed away from the railing and walked toward them; it only took a few minutes for him to reach them.

He looked grim. “He’d disappeared by the time I got here.”

Leonora sagged. “So it’s a dead end—we’ve lost him.”

“No,” Tristan said. “Not quite. Wait here.”

He left her with Deverell and crossed the road to where a streetsweeper stood leaning on his broom midway down the short street. Reaching under his scruffy coat, Tristan located a sovereign; he held it between his fingers where the sweeper could see it as he lounged on the rails beside him.