It wasn’t until the first body was found that anyone took the film seriously. A link to a video clip on YouTube had been sent to the public email address of the National Criminal Investigation Department. The email contained no message, and the sender was impossible to trace. The police administration secretary did her job, followed the link, watched the film, and assumed it was a rather baffling joke, but nonetheless entered it in the records.

Two days later three experienced detectives gathered in a small room on the eighth floor of National Crime headquarters in Stockholm, as a result of that very film. The oldest of the three men was sitting on a creaking office chair while the other two stood behind him.

The clip they were watching on the wide computer monitor was only fifty-two seconds long.

The shaky footage, filmed in secret on a handheld camera through her bedroom window, showed a woman in her thirties putting on a pair of black tights.

The three men at National Crime watched the woman’s peculiar movements in embarrassed silence.

To get the tights to sit comfortably she took long strides over imaginary obstacles and did several squats with her legs wide apart.

On Monday morning the woman had been found in the kitchen of a terraced house on the island of Lidingö, on the outskirts of Stockholm. She was sitting on the floor with her mouth grotesquely split open. Blood had splattered the window and the white orchid in its pot. She was wearing nothing but a pair of tights and a bra.

The forensic post-mortem later that week concluded that she bled to death as a result of the multiple lacerations and stab-wounds that were concentrated, in a display of extraordinary brutality, around her throat and face.

The word stalker has existed since the early 1700s. In those days it meant a tracker or poacher.

In 1921 the French psychiatrist de Clérambault published a study of a patient suffering from erotomania. This case is widely regarded as the first modern analysis of a stalker. Today a stalker is someone who suffers from obsessive fixation disorder, an unhealthy obsession with monitoring another individual’s activities.

Almost 10 per cent of the population will be subjected to some form of stalking in the course of their lifetime.

The most common form is when the stalker has or used to have a relationship with the victim, but in a striking number of cases when the fixation is focused on strangers or people in the public eye, coincidence is a key factor.

Even though the vast majority of cases never require intervention, the police treat the phenomenon seriously because the pathological obsessiveness of a stalker brings with it a self-generating potential for danger. Just as rolling clouds between areas of high and low pressure during stormy weather can suddenly change and turn into a tornado, a stalker’s emotional lurches between worship and hatred can suddenly become extremely violent.

1

It’s quarter to nine on Friday, 22 August. After the magical sunsets and light nights of high summer, darkness is encroaching with surprising speed. It’s already dark outside the glass atrium of the National Police Authority.

Margot Silverman gets out of the lift and walks towards the security doors in the foyer. She’s wearing a black wrap cardigan, a white blouse that fits tightly at the chest, and high-waisted black trousers that stretch across her expanding stomach.

She makes her way without hurrying towards the revolving doors in the glass wall. The guard sits behind the wooden counter with his eyes on a screen. Surveillance cameras monitor every section of the large complex round the clock.

Margot’s hair is the colour of pale, polished birchwood, and is pulled into a thick plait down her back. She is thirty-six years old and pregnant for the third time, glowing, with moist eyes and rosy cheeks.

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