‘A letter? My wife said there was a letter threatening to kill her.’

Frost showed it to him. His face went white. ‘Why are we being persecuted like this?’ He sank down into a leather armchair. His wife dropped down on his lap and snuggled up to him.

‘That’s what I want to know,’ said Frost. ‘Why?’ He and Gilmore were sitting, facing the Comptons, in a large leather settee. He fumbled for his cigarettes. ‘Whoever’s doing this must have a reason.’

‘Reason?’ said Compton ‘There’s no bloody reason. It’s the work of a maniac.’

‘We’ve been receiving a spate of complaints about poison pen letters. “Did you know your wife’s been having it off with the milkman?” – that sort of thing. I’m wondering if it could be the same bloke.’

‘We’ve had death threats, Inspector, not stupid poison pen letters.’

‘Run through the main course of events again,’ said Frost. ‘Just for the benefit of my new colleague here.’

Mark Compton slipped his hand under Jill’s house-coat and gently stroked her bare back. ‘OK. As you know, we run a business from this place… Jill was on her own one night when this bugger phoned.’

‘What sort of business is it?’ interrupted Gilmore.

‘Dirty books,’ said Frost.

Compton glowered. ‘We’re fine art dealers,’ he corrected. ‘Mainly rare books and prints, a small proportion of which might be termed erotica, and manuscripts, but not many. There’s over a quarter of a million pounds’ worth of stock upstairs.’

Gilmore whistled softly to show he was impressed. ‘Safely locked up, I hope?’

‘We couldn’t get insurance if it wasn’t,’ Compton replied icily. ‘Your Crime Prevention Officer has given us the once-over and was quite satisfied. We’ve got a sophisticated alarm system with automatic 999 dialling. If anyone tried to break in, they’d set off the alarm at your police station.’