The shop that stocked the crackers was in East Finchley, a suburb in the north London wilderness that Dempsey hadn't visited before. He walked along, shoulders hunched against the cold. It was December 19, a bitter day. The trees in the park to his left were leached of colour and the sky was leaden: he could smell snow.

He was not in a good mood. After leaving the hospital, he'd gone straight to the SI-10 office and picked up the brief. He was unshaven and sore from his snatched hours of sleep on the hospital chair, and his neck ached like hell.

Harry had barely escaped with her life last night. Damn it, he had known her going under cover was just too dangerous – a step too far. Try telling her that - or anything else - at the moment, though. The best way to ensure she did something was to tell her it wasn't a good idea. Beneath the multitude of surface differences the two of them were curiously similar, he thought: wilful, stubborn and determined; never mind that she prided herself on doing things by the book while chastising him for his more intuitive approach.

Seeing her lying on the pavement with the blood running down her temple had been terrible. Later, when he knew she was alright, he had sat for a long time, watching her sleep and trying to sort through a mixture of emotions: anger, yes – but also the overwhelming awareness that losing her would be devastating. He had been conscious that he was in love with her for some time; certainly since the night they had spent together. But this knowledge only seemed to serve to make their relationship more fraught. They argued constantly, stuck in a terrible impasse. And when something like this happened… it devastated him in a way that he knew affected his ability to be circumspect, to focus dispassionately on the job. But what was the alternative? Leave and never see her again? He wasn't yet ready to consider that as an option.

He had reached the shop. Bojangles, the sign above the door said, and underneath: Specialists in unusual and high quality toys and games. The window was crammed with toys of all shapes and sizes: dolls, teddy bears, train sets and brightly coloured bouncy balls. Tinsel and fake snow adorned the display to add a festive feel. The interior brightly lit and looked inviting. Grateful to get out of the cold, Dempsey pulled open the door.

Inside was a maze of shelves. Plush animals spilled from boxes, and a beautiful wooden train set was laid out in an intricate display on the floor, accessible to children. There were no other customers, and the small counter towards the back was unstaffed. Dempsey wandered around. His gaze fell on a prominent Christmas rack by the counter. On the bottom were boxes of handmade crackers. He moved forward for a closer look.

As he bent down, he heard a cough. A tall, gangly youth of about 18, with a smattering of pimples and red curly hair, had appeared from a back room. He smiled politely at Dempsey.

"Good afternoon. Can I help you?"

He was aware he probably wasn't the shop's usual type of customer.

"Afternoon. I was wondering if I could have a look at some of these crackers you have down there."

'Of course," the boy hurried around the counter. "How many were you looking for…?"

He lifted up one of the buff-coloured boxes. There were 12 crackers visible in the clear window, their bright glowing colours contrasting pleasingly with the dull packaging. He handed it to Dempsey.

"These are quite unusual you know. All hand made by a lady in Wales. We've been stocking them for a few years. They cost a bit more than the mass produced ones, but they're very popular."

Dempsey felt the weight of them. Substantial. "Can I ask your name, son?"

"It's Jack."

"Pleased to meet you Jack, I'm Lieutenant Dempsey. The thing is, I'm not strictly looking to buy crackers today. I'm a police officer and I'm investigating a crime. I'm interested in the toys that may be contained in these crackers."

Jack blinked at him. "Oh – I see."

He nodded. "It's not very festive, sorry. In particular, I'm interested in some rings – women's rings?"

"I know the ones you mean - plastic, with sparkles? They come in different colours. Little girls love them. We sell them on their own too." He gestured towards another display. Dempsey went over to have a look.

"Say, Jack. Don't suppose you keep sales records here, do you? Or maybe you have a list of regular customers? I'd be interested to know if there was anyone who was buying these, maybe in bulk?"

The boy shook his head. "I have to tell you Lieutenant, I'm very curious. Can I ask what this is connected to?"

"'Fraid not. Let's just say it's important."

"I'm sorry, I only work here a couple of days a week. The owner, Mr Jenkins, might know more. He's in the back at the moment, doing the accounts. I can go and get him if you like."

"Sure, that'd be great, thanks."

Jack turned to leave but before he could, an older, mild-mannered-looking man appeared in the doorway to the back of the shop. He was dressed a brown cardigan and thick glasses.

"Is everything alright, Jack?" he enquired, looking quizzically at Dempsey.

"Oh, hi Mr Jenkins," Jack began, "I was just coming to find you. Lieutenant Dempsey here's a police officer. He's investigating a crime and he's got some questions about those rings we sell, the ones that go in the Welsh crackers. He wondered whether we keep a record of people who've been buying them."

Mr Jenkins considered Dempsey over his spectacles. "Oh yes? Well, I might be able to help, Lieutenant. I do keep records of some of our more regular customers. Marketing purposes, you know. We send out newsletters occasionally. I can check back through the records to see whether anybody has bought crackers or rings of late."

He pulled out a large hard back log from underneath the counter and came around to join Dempsey. Jack had disappeared. Dempsey watched as he began to flick through the pages.

"You been in this business long?" he asked.

"Years. I fell in love with toys and games from an early age."

"Get much trade, tucked away in this corner of the world?"

"Oh, people find us somehow. You'd be amazed."

He glanced up, looked at Dempsey levelly. Dempsey gave him a mild grin, but here was something about the man's eyes he didn't like. He wasn't sure whether he'd want any kid of his hanging around in here.

His eyes fell to the log book as Mr Jenkins turned the pages slowly. They were crammed with neat handwritten notes; lines and lines of meticulously logged purchase information.

Something was niggling the back of his brain. The handwriting – there was something familiar about it. As if he'd seen it before, maybe in a dream. The way it sloped sideways… it was distinctive. Then it came to him.

I just wanted to tell you how much I'm enjoying my work, especially at this wonderful time of the year.

He had a flush of understanding. Mr Jenkins: middle-aged, mild mannered. As if reading his thoughts, the man looked up at him and smiled.

"Lieutenant?"

What had Harry said? "His eyes… I've never seen anyone so cold." He knew what she meant now. They stared at each other for a second, and then Dempsey's hand flew towards the pistol under his jacket.

But Mr Jenkins was quicker.