Katie was sitting in the canteen with a cup of tea and a hand pie when Detective Inspector Fitzpatrick, Detective Cullen and Bill Phinner came looking for her.

The rain was trickling down the window beside her. She was reading the latest report on Oberstown Children’s Detention Campus in Lusk, where seventeen-year-olds were sent by the courts these days instead of adult prisons. Last week there had been an outburst of serious violence there, including a stabbing in which a boy had lost one of his eyes – not at all like the TV comedy series The Young Offenders.

Eighteen months ago, in Cork, she had set up her own specialized team of young detectives to investigate juvenile crime, headed up by Detective Sergeant Alanna McPhail. So far they had made good progress in bringing down the incidence of petty theft and clashes between rival gangs and drug-peddling. But Katie was keen to know how well the young offenders were being rehabilitated, or if they were simply going to come strutting back from Lusk even more hardened and antisocial than they were when they went in.

‘Sorry to interrupt your lunch, ma’am,’ said Bill. ‘I’ve heard back now from my team who’ve been searching James MacGreevy’s house. So far they’ve come up with nothing that could possibly be bomb-related. Not even a clock or a box of matches.’

Katie raised an eyebrow. He was usually so miserable that she could always tell when he was feeling pleased with himself.

‘You’ve come up with something, though, haven’t you?’

Bill held up two printouts, one with rainbow-coloured stripes on it, and the other with three columns of figures. ‘These here – these are the DNA tests on the sample of hairs that we clipped from MacGreevy’s dog. We compared them with the hairs we found stuck to the parcel tape that was used in making the bomb. The probability that they belong to the same dog is ninety-nine point nine-nine per cent.’

‘So – whoever planted it – it’s almost certain that MacGreevy made it.’

‘He’s been downstairs for a while now, ready to be interviewed,’ said Robert. ‘He’s called in his own solicitor, too, and no prizes for guessing who that is.’

‘Don’t tell me. Aidan O’Mahoney.’

Katie knew Aidan O’Mahoney well: he had a long record of defending Republican activists. It was in his blood. After the IRA had ambushed a detachment of British soldiers at Dripsey in 1921, his great-great-uncle Patrick O’Mahoney had been caught, tried, and executed by firing squad at Victoria Barracks, and the O’Mahoney family had nursed a grievance about it ever since – a grievance that had smouldered down the years like a peat fire, occasionally dying down but never completely going out.

‘Go on, finish your pie, ma’am,’ said Robert. ‘We can wait.’ But Katie pushed her plate away, picked up her purse and stood up.