The office in 18 Denmark Place could by no means be described as luxurious. In fact, even just saying it was comfortable would have been a stretch. The clanging metal stairs, the dirty bathroom, the farting sofa and the ugly file cabinets added up to give a feeling of bare, cheap functionality. And yet, Robin Ellacott loved it dearly. It was the symbol of the fulfilling of her dream of being a detective – or at least an assistant detective.

It could not be denied that a great part of Robin's job was made up of essentially secretarial tasks: welcoming clients, making coffee and tea, dealing with emails and letters. But she enjoyed this too, particularly the mail. Some messages, admittedly, were downright boring: long rants on husbands or wives suspected of cheating, lamentations on allegedly stolen animals ("We're not going to investigate a missing parakeet" had said Strike resolutely, after she had read him an especially dramatic email. "I still have a dignity of sorts"). Some others, though, were genuinely interesting: either because they brought on some real investigating, or because they were written by absolute lunatics.

Robin had learned not to be discomposed by this kind of letters. She had initially found very difficult to believe that Strike could be so nonchalant when it came to the death threats and the intimidations he seemed to receive alarmingly often, but she had come to understand that it was no more than an occupational hazard for him, and that they were mostly empty threats anyway. In time, she had developed some sort of black humour and had even found herself smirking when receiving such a letter or while reading it to Strike, as she occasionally insisted to do.

He never bothered to read the letters from his usual haters, whom he could recognize at a glance: the one who wrote on pink paper, the one who used red ink and wrote in capitals, and so forth. Strike used to keep these letters all jumbled together in a drawer of the metal cabinets behind Robin's desk, and he had begun to call it 'the nutter drawer' in an attempt to amuse Robin, when she had begun working for him and had been affected by their arrival – Strike knew that she had been, although she had tried her best to act indifferently. At first, Robin had avoided to use the nickname, lest she should appear unprofessional. All the same, it had stuck and it had become a bit of a private joke between her and Strike.

Robin would never have said it out loud, especially within earshot of Matthew, but the nutter drawer was perhaps her favourite part of the dingy office in 18 Denmark Place.

Robin's first anonymous letter had arrived three days after she had begun working for Strike. On that Thursday morning, she had climbed the clanging stairs up to the office, only to find the door locked and a Post-It pasted on the glass panel: "Back soon".

She had been disappointed, at first, at being locked out of her own workplace, but after some deliberation, she decided that Strike must have darted out of the office on some urgent business: to follow someone maybe, or to capture some dangerous criminal. That was probably it. In fact, it had been very considerate of him to leave her a note, what with the ordeal he must certainly be dealing with.

Satisfied with this reconstruction of the events, Robin decided to wait, leaning on the wall and reading the bride magazine she had bought on her way to work. The thought of going for a coffee to pass the time had struck her, but she had felt it would have been wrong to sit in a café while her boss was out there, fighting crime.

Opening her brown leather bag - a gift from Matthew for her last birthday - to fetch the magazine, she happened to glance at the doormat and noticed three letters sitting there.

She picked them up, resolving she might as well make herself useful and deal with them there and then. The first letter, she saw, was from a bank. Tactfully, Robin left it unopened – she supposed that Strike, who worked in a shabby office and probably slept in it too, was bound to have some economic problems.

She passed on to the second letter: it was a disgruntled note from Mr. Gillespie, whom Robin knew already after only three days of work, because he phoned daily about the rent and she had precise instructions to tell him that Strike wasn't in.

With a sigh, Robin concentrated on the third letter. There was no address, so she supposed that it had been delivered by hand, and it was, curiously enough, pink. It even had a kitten printed on a corner of the envelope. Raising her eyebrows, she extracted from the inner pocket of her purse a small Swiss Army knife and cut it open. The sheet of paper inside was equally pink, and written in blue ink. It read: "You do not know what is coming to you. You think you are smart, but you are just a big fat cripple. You watch your back".

Robin gaped. She couldn't believe her eyes. It was a death threat! And she had touched it with her bare hands! What if there were fingerprints and she had confused them or deleted them with her own? Well, she had to call the police. No, it was better to call Strike first. Or perhaps text him? If he was following someone, he probably couldn't answer the phone. Still, this was an emergency. She couldn't very well text him something like "Sorry to bother you, but a death threat just arrived. See you later". She had to call him. She rummaged in her bag, grasped her mobile, and was about to hit the 'Call' key when she heard the unmistakable, uneven thumps of Strike's steps on the metal stairs.

He appeared, backpack on one shoulder, a plastic bag in one hand, holding the handrail firmly with the other. "Sorry I've left you out" he said, inserting the key in the lock. Then he noticed Robin's shocked expression. "What is it, what happened?" he asked, suddenly sharp.

Robin tried to pull herself together. "I think we should talk about it inside" she whispered.

They entered the office, Robin still clutching the letters – although she had slipped the pink one between the other two to avoid touching it directly – Strike looking vaguely bemused.

"Well?" he demanded.

"This has just arrived. I think we must call the police at once". She handed him the three letters. Strike looked at them. "You think we should sue Mr. Gillespie for harassment? He certainly does seem to be stalking me-"

"I meant the pink one!" cried Robin, affronted. Strike took it and read it quickly.

"Oh" he said simply. "I'm sorry, I forgot to warn you".

"Warn me?"

"This sort of letters arrives quite often. This particular bloke – yes, he's a bloke – who uses pink paper writes almost every week. He's probably the funniest".

"The funniest?" Robin realized that she kept repeating what Strike said, but she couldn't help it. She was completely nonplussed. He seemed to find the whole thing amusing.

"Well, it's like being threatened by a five-year-old, isn't it? 'Big fat cripple', indeed!" Strike chuckled. Then he noticed Robin's hurt look and stopped.

"Listen" he said in a conciliatory tone "I told you, it happens often enough. They're just nutters, they write because they are too scared to act. They'd never be able to confront me on whatever grudge they're holding against me. Next time, just chuck the letters in that drawer over there and don't give them a second thought".

"You keep them, even if they are insignificant?" countered Robin, who was feeling sillier by the minute.

"Well, it's only professional, isn't it?" replied Strike, with the faintest trace of a grin.

Robin blushed and, desperate to change the subject, she said: "How did your morning job go?"

"What morning job?"

"I thought... I thought you were out for some investigation or other this morning, since you weren't in the office" she explained, wishing she had shut up.

"Oh, I see". Strike was doing his utmost not to laugh. She certainly was an enthusiast, this one. He hadn't missed her attempt to preserve the threat letter from fingerprints by putting it between the other two. "I wasn't out on detective work. I went to get some breakfast" he said, lifting his plastic bag with a light smile.

Robin wished the earth would open and swallow her. "Right. Yes. Of course. Well, I'll let you eat in peace. I'll just file the letter in that drawer then, shall I?" she said, all the while staring at the empty computer monitor, too embarrassed to look at him.

"Yeah" Strike put the letter on her desk. "Drop it in the nutter drawer, and forget about it". He turned and, limping slightly, he walked in his office, closing the door behind him.