There was a safe set into the wall behind a framed hunting print over a cast-iron fireplace; Hennessy opened it and took out a brown A4 manila envelope. He flicked the open end with a thumbnail as he walked over to the desk. Inside was a sheaf of papers, each a report on an individual arms cache. There were fifteen in all, and he was expecting a further six by nightfall. He spread the sheets out on the desk and examined them. Three of the caches had been interfered with. In all, fifteen kilograms of Semtex had been taken, along with a dozen detonators, two mercury tilt switches, two handguns and a small amount of ammunition. Everything else necessary for the construction of bombs – wires, timing devices, transmitters – could be bought from High Street stores. Hennessy was sure that the maverick IRA team had been stealing from the organisation’s munition dumps and he was equally certain that they were being helped by somebody inside the organisation. The trouble was that there was no pattern, no connection between the three dumps. They were the responsibility of three different IRA cells. He grunted and gathered up the papers. Jackie lifted her head and watched him put the sheets back into the envelope.

‘Maybe the remaining inspections will supply the answer,’ he said to her and she chuffed in agreement.

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.’