Hennessy heard a car arrive outside and footsteps crunching on the gravelled drive before the doorbell rang. He waited to see if Mary would answer it, but he wasn’t surprised when she didn’t. He went and opened the door to let in Kavanagh and Murphy and a small sharp-faced man with a straggly moustache and grey, watery eyes, Willie O’Hara. Jimmy McMahon stayed outside in the Jaguar, reluctant to let it out of his sight. Willie was wearing his normal baggy grey suit, the trousers held up by a greasy brown belt, and he was carrying a paper bag. Hennessy took the three men into the study. ‘Was the car clear?’ he asked O’Hara.

‘Other than this?’ answered the little man, holding up the bag. ‘Yeah, this was all, but it would’ve been more than enough.’ He reached in his hand and took out a coil of black wire and held it out to Hennessy. ‘Crude, but it would’ve done the job.’

There were two pieces of wire, each about ten-foot long, and both had been soldered to the flash-bulb.

Hennessy pointed to the red powder which covered the flash-bulb. ‘What’s this?’ he asked.

O’Hara’s eyes shone. ‘Ground up match-heads,’ he said. ‘Mainly potassium chlorate. Just to add an extra kick. Probably wouldn’t have been necessary, but it’s a nice touch.’

‘How does it work?’

‘Whoever it was had prised open the fuel cap and left the flash-bulb dangling just inside the tank, in the fumes above the petrol. You turn the key and up she goes.’

‘Guaranteed?’

O’Hara frowned, wondering what Hennessy was getting at. ‘Pretty certain. I mean, it’s not the sort of gadget we’d use because there’s always an outside chance that the bulb might fall into the petrol in which case it wouldn’t ignite it. And it’s also pretty easy to spot.’

‘A warning?’

O’Hara nodded eagerly. ‘Yeah, that’s exactly what I was thinking. Is somebody giving you trouble?’

‘I’ve an idea who it might be, yes. Willie, thanks for your help.’ Hennessy shook him by the hand and showed him out, telling Jimmy to drive O’Hara wherever he wanted to go.

Back in the study he sat behind his desk and told Kavanagh and Murphy to make themselves comfortable. He offered them tea or coffee but they declined. He didn’t offer them anything stronger because even under stress Kavanagh didn’t touch alcohol and he could already smell whiskey on Murphy’s breath and they’d all need clear heads.

‘I’m coming round to thinking that maybe you were right about what you said yesterday, Jim,’ Hennessy said to Kavanagh.

‘About going to the farm?’