"What do you mean we can't call the police?" Sam demanded.
"I recognise the boy with Wai-hung," Ethan said, pointing at the screen of Sam's laptop.
Software Ethan had installed on his own laptop before it was stolen was now sending them the images captured by its camera - revealing who was using the computer.
"Good!" said Jenny. "And I recognise where they are. That mall is in Shek Kip Mei. So..."
She was interrupted, however, by the sound of a hissed warning coming from Sam's laptop: "Police!"
Almost immediately the image on their screen narrowed then disappeared as the lid on Ethan's laptop was slammed shut.
Wai-hung stood up to scan the river of people flowing through the mall's concourse and pooling around its exits and escalators.
Confused, he turned to Yiu-hon. "Where ...," he began, before realising Yiu-hon was clutching the stolen laptop to his chest. Instinctively, he reached to take it back ... but then thought better of it.
Although he couldn't see any police, why should he take any chances? If they saw him, he knew they would be all over him - checking his ID and asking questions. And if he was found in possession of the computer ...
Instead, he'd let Yiu-hon take the risks. That's what Wai-hung kept him around for, wasn't it?
So, shoving Yiu-hon aside, he walked as quickly but inconspicuously as he could in the other direction.
"We know who the thieves are, where they are and that the police are nearby," Sam told Ethan.
"So ... what part of getting your property back don't you like?" demanded an exasperated Jenny.
"I told you," Ethan said quietly. "We were friends when we were little."
"And did this Yiu-hon steal your toys then, too?" Jenny asked.
"We don't know he stole my laptop," Ethan muttered.
Jenny pointed at the screen. "I think we do."
"But if he didn't, he doesn't have anything to fear from a chat with the police, does he?" Sam asked.
"But if he is in any way involved, they'll send him straight back to the young offenders' institute," Ethan said. "When you've been in trouble once, they don't ask too many questions the second time."
Sam stared at Ethan. "Back? He's been to jail before?"
Ethan nodded. "Look ... you don't know what his life's been like."
"Oh, now he's the victim here, is he?" Jenny asked.
"He pleaded guilty but I'm sure Wai-hung was behind that, too."
Jenny shook her head in disbelief. "Well, at least there's one thing we can say in Yiu-hon's favour then - if he's gone straight out stealing with Wai-hung again, he's not the type who holds a grudge."
Ethan had known Yiu-hon since they were toddlers. They had played together on the estate - with Ethan always bossing his sweet-natured friend around - and started at primary school in the same class.
But by the age of nine they were seeing less and less of each other. While Ethan was already a rising academic star, Yiu-hon was beginning to miss days at school. Although excuses were made for these absences, many on the estate believed that, with a compulsive gambler for a father and a mother who had disappeared the year before, the die was already cast.
As he sat looking at his mother sleeping in her hospital bed, Ethan realised, despite everything that had happened to him, he'd been astonishingly lucky to have been raised by someone like her.
Whereas he knew, whatever Sam and Jenny said, for Yiu-hon there would never be any real justice in life - whatever crimes he had or hadn't committed.
But, but, but ... with money so tight at home, Ethan also recognised it would be unfair to ask Grandad to right the world's wrongs and simply pay for a new laptop.
In the darkness, Ethan fumbled to find the lock with his key. He hoped the light on the walkway outside their flat would soon be fixed but, even more fervently, he wished he didn't have to phone the police once he got in.
When the key eventually did turn and the door opened, Ethan found himself tripping over something.
Switching on the light, he saw a bulky plastic bag lying on the doormat. Inside was his laptop.
Yiu-hon! That fool was becoming a liability. While he hadn't wanted him to get arrested - the trail might have led back to Wai-hung, after all - he didn't expect the idiot to just throw a laptop into a rubbish bin.
Yiu-hon's story was that, after they'd split, the police had spotted him and he'd had to ditch the computer before they'd stopped him. However, when he'd taken Wai-hung back to the bin, it wasn't there.
Of course, Wai-hung had called him a liar and searched his place. But after finding nothing, he now believed Yiu-hon when he said he didn't have it.
Although Ethan felt certain he knew who had returned his computer, when he told Sam and Jenny what had happened, he didn't try to dress up the indecisiveness he'd shown as good judgment.
During the next couple of weeks Ethan didn't see Yiu-hon - or Wai-hung and the rest of his gang - around the Ki Lung Estate. Maybe this was because of the increased number of police patrols - or maybe it was because Wai-hung's criminal activity now took him further afield.
Anyway, Ethan didn't know and didn't care. There was so much work still to do on the Shamefacebook site. Sam had come up with a couple of good ideas for improving its functionality and Ethan and Jenny were kept busy writing the code to implement them.
Like much else on the estate, the ageing lift in Ethan's block had seen better days. As Ethan got in one afternoon, pre-occupied with a bug in the website's code, he didn't see Wai-hung bearing down on the still open doors until the last moment.
Ethan's repeated jabs at the "close" button met with the usual delayed response, and Wai-hung managed to get a foot wedged in the narrowing gap. The doors groaned and protested as they re-opened.
Wai-hung got in, shoving Ethan in the chest. "What's the matter with you, didn't you see me?"
Ethan said nothing. Wai-hung seemed even more agitated than usual, he noted nervously.
Wai-hung thumped the button for the floor above Ethan's. "Come on," he insisted angrily.
As the doors closed, Ethan instinctively felt for the bag hanging from his shoulder. Amidst the school books inside was the laptop Wai-hung had tried to steal from him.
Full of restless energy, Wai-hung spotted the protective movement. "What's in there?" he demanded.
As Ethan felt the sweat begin to trickle down his back, to his consternation the lift suddenly lurched to a halt between floors. He was trapped.
To be continued next week