‘And GHB is illegally produced just to be used as a date-rape drug?’ Fabel asked.

‘No. Actually, it is very popular on the clubbing and rave circuit. It is used a lot as a downer to bring people down from Ecstasy and cocaine highs. I’m sure your own drugs squad will have had a lot of experience of it in the Hamburg club scene.’

‘How would it be ingested? Is it flavourless, like Rohypnol?’

‘Almost. When diluted, it has a slightly salty taste. In fact, one of the street names for it is Salty Water. Apart from that, it would be pretty easy to administer it in an alcoholic drink, which would synergise its effectiveness, or as a powder hidden in food.’

‘Michaela just told us she was at a club and some guy gave her water to drink and she thought it tasted salty.’

‘That would probably be it.’

Fabel looked down at Stern’s report. ‘What about the rape? Did we get any forensics?’

‘All we can say is that she was vaginally raped over a period of two to four hours … perhaps by more than one man. No sodomy. No forced oral sex. And, unfortunately, no semen for DNA analysis. He – or they – must have used condoms. She was not beaten or otherwise abused. The only other injuries were the ligature marks on her ankles and feet …’ Stern nodded towards the file in Fabel’s hands. ‘The pictures are in there.’

Fabel opened the report. The photographs showed the marks on her wrists and ankles. She had been spread-eagled, like the murder victims. But Michaela was alive. There was another photograph, of a woman’s forehead with the blonde hair pushed back to reveal a faint but discernible red mark.

‘What’s this?’

Stern smiled. ‘That, Herr Kommissar, is a clue the rapist or rapists didn’t intend you to see. Michaela has highly sensitive skin, she has an eczematous condition. That’s one of the reasons for her tan – UV therapy.’ So much for my sun-salon theory, thought Fabel. ‘Anyway,’ continued Stern, ‘whoever did this to her made some kind of mark on her forehead. They have obviously tried to clean it off, but Michaela’s sensitive skin reacted to the paint or whatever it was they used. I thought it was very significant so I included it in the standard rape-kit evidence photographs, even though it isn’t much of an injury.’

‘And I’m very glad you did, Herr Doktor,’ said Fabel. ‘This could be of enormous significance evidentially.’

‘It looks like an X to me,’ said Stern. ‘Any ideas what it could mean?’

Fabel looked at the mark and frowned. ‘As a matter of fact I do … I think that it is a Futhark symbol.’

Stern shrugged his incomprehension.

Susanne moved over to Fabel, who angled the image towards her. ‘A Viking rune?’

Fabel nodded and slipped the photograph back into the file.

Saturday 14 June, 3.50 p.m. Övelgönne, Hamburg.

Susanne leaned over and kissed Fabel, stroking his cheek before getting out of the car.