‘No, of course not. He’s far too old for me.’ Out of sight of the children, Tilsner gave her a nasty squeeze on the thigh.

Ouch, she mouthed at him, silently.

‘Anyway,’ she continued. ‘You’ve met Werner before, when we lived in Berlin. We work together in the People’s Police.’

‘Is he your boss then?’ asked Johannes.

Tilsner couldn’t help guffawing at this. ‘No, young man. She’s my boss.’

‘Women can’t be bosses,’ said Johannes.

‘Yes they can!’ shouted Jannika, punching her brother on the leg. He pinched her in return, provoking a yowl.

‘Stop it you two, this instant,’ said Müller. ‘Otherwise I’ll take you straight back to the school. And anyway, it’s not that unusual to have women in charge these days. Once Jannika grows up, there’ll be women bosses everywhere.’ Then she added, sotto voce, for Tilsner’s sole benefit: ‘And the world will probably be a much better place as a result.’

Müller hadn’t warned her adoptive mother about the visit, so Rosamund was all over the twins, offering them sweets, cakes and juice, even though they’d all be having supper within the hour.

It gave Müller and Tilsner the chance to look through the contents of Frau Voights’s briefcase – or perhaps more accurately, Heinz Schenk’s briefcase, as it had clearly been the director who’d collected all the information.

‘She seemed very upset,’ said Tilsner as they laid out all the sheets of photocopied paper on the kitchen table. ‘More than many workers would be when their boss commits suicide.’

‘I really don’t think he was just her boss, do you?’

‘Lovers?’

‘Without a doubt. She was a broken woman. And she was taking a huge risk giving us these. What if we were secret Stasi agents . . .’ Müller paused, smiling evilly at her deputy. ‘Of course, in your case . . .’

‘Give it a rest, Karin,’ snapped Tilsner.

Müller laughed. ‘Anyway, I’ve no doubt they were in a relationship. Which is why Jäger’s claims about Schenk and Achterberg’s sexuality seem so patently absurd.’

She shuffled the papers in front of them into something approximating date order, and then tried to make head or tail of them.

There were various initials – which could be acronyms for chemicals, or for pupils, or perhaps there was a mixture of both. And then various percentages and dates. But – as Frau Voights had predicted – to both Müller and Tilsner they were meaningless.

Müller had faith that Schmidt would be able to make more sense of them once they were back in Dresden.

What she did know, without doubt given the way the woman had been acting, was there was something sinister in these pages. Voights had assured her that her own children were too young to be at risk – Müller wasn’t so sure.