Their route took them down a street lined with elegant nineteenth-century buildings. There weren’t many other people around, early on a Friday morning, so Ket Siong took note of the guy walking behind them. He was in a light grey puffer jacket and jeans, with a bulky cross-body bag slung over a shoulder. Asian, but what kind of Asian was hard to tell, thanks to the cap pulled low over his face.

Ket Siong wasn’t in a temper to pay attention to anything that wasn’t Renee, but it struck him that there was something vaguely familiar about the man. They’d passed the Zambian High Commission and the Korean Consulate when he worked out where he’d seen the guy before.

There had been a man in a light-coloured puffer and a cap, with a cross-body bag, in Hyde Park yesterday. Ket Siong had passed him just before he’d seen what had turned out to be Renee, hunkered down on the path.

There began to be, in Ket Siong’s mind, something that was not quite suspicion, but the hazy outline of a question mark.

He turned his head to slide a look at the man out of the corner of his eye. The man sped up, overtaking Ket Siong and Renee on the pavement.

Something about this, and the way the man was holding his shoulders, solidified Ket Siong’s growing suspicion.

“Excuse me,” he said.

Renee glanced up at him, surprised.

The man’s pace quickened.

Ket Siong raised his voice. “Excuse me.” He let go of Renee’s hand, taking a step towards the man.

The man broke into a run.

Ket Siong did not pause to think about what he should do next. He lunged after him. But the man had about a yard on Ket Siong, and he was fast, despite the bag bumping on his back. He pelted down the street, running flat out.

Ket Siong was at risk of losing him, when a van pulled out of a driveway ahead of them. The man checked, stumbling. That delayed him just enough for Ket Siong to get close. He threw himself at the man and they went down together.

The man jarred his shoulder against the pavement, swearing fruitily in Cantonese. His accent sounded Malaysian, but Ket Siong had assumed it would.

“Why were you following me?” he said, in the same language. “Who are you?”

“Motherfucker! Are you crazy or what?” said the man. “I’m not following you. Who the hell are you? Get off me!”

He tried to throw Ket Siong off. Ket Siong slammed him back to the ground and said, “I saw you last night, at Hyde Park.”

“So what if I was at Hyde Park?” said the man belligerently. “Are you the only person who’s allowed to go to Hyde Park?”

Renee caught up with them, looking alarmed. “Are you OK? What’s going on?”

Ket Siong switched to English for her benefit.

“If you weren’t following me,” he said, “why run away when I called after you?”

The man glowered. “Let go!”

“I’ll let you go if you answer me,” said Ket Siong. “Who told you to follow me?”

“I don’t know what you are talking about.”

“Was it Low Teck Wee?” Another possibility occurred to Ket Siong, far more disturbing. “Are you Special Branch?”

Ket Siong would have expected this to elicit a furious denial, if it was anywhere near to the truth. The man’s expression was reassuring: he merely looked baffled.

“Special Branch?” he said. His eyes flicked to Renee. “Special Branch also wants to follow you? For what?”

“What’s in your bag?” said Renee.

The bag was under the man’s body. Ket Siong hadn’t thought to look in it. There was a minor scuffle while he remedied the oversight.

“Don’t break!” said the man. “It’s expensive!”