For the stake-out team it was business as usual. The only break from routine came when Andrew Harvey left home alone in the Toyota. The Transit van was parked 200 yards away in the drive of an unfinished house at the top of the cul-de-sac in which the Harvey villa was situated.

When Harvey cleared the house, Maggie Rose slipped from the van and gunned her MG Metro, parked out of the line of sight, into life. She had the Toyota in view as it reached the roundabout leading to Wardpark and Castlecary, but there were no surprises in store. Harvey drove straight to the factory, and drew up in its car park, alongside other vehicles. Six-day working, thought Maggie, the software business must be doing well.

Joy Harvey left half-an-hour after her husband, in a red Ford RS 2000 with a new ‘M’ prefix. McGuire followed her at a distance in the Transit. He was led into a covered car park beneath the sprawling Cumbernauld Town Centre.

As he pulled up, he saw Joy, her long legs carrying her at a brisk pace towards the Asda foodstore. He waited for a full minute before strolling absent-mindedly towards the supermarket. He took a trolley, and wheeled it casually along the first aisle, an inconspicuous unaccompanied male, one of several, picking items at random from the shelves. He spotted her easily, as she moved purposefully from section to section. Her trolley was almost filled to capacity with food, toiletries and kitchenware. ‘Those two fairly go through the groceries,’ McGuire muttered to himself. Eventually he saw her head towards the checkout, the trolley overflowing. He left his, and retraced his steps, as if to pick up a forgotten item. Then, slapping his jacket and swearing softly, as if he had forgotten his wallet, he spun on his heel and walked quickly out of the store.

He was back in the Transit, observing the Ford through its wing-mirror, by the time Joy returned. Eight Asda carrier bags were crammed into the trolley. She folded down the back seat and began to pack the car. McGuire noted that one of the carriers appeared to be filled entirely with toilet tissue and kitchen rolls. Two others contained cartons of orange juice, milk and various soft drinks. Another was full of fresh fruit.

Before she had finished loading her car, McGuire started the van and drove off. He was back on station well before she returned home. He called Maggie again.

Her car-phone rang out, then was answered. ‘How’s it going, sarge?’

‘Quietly. Our boy’s at work. How about you?’

‘We’ve been to Asda. Joy did a food-shop. Enough to feed a family of six for about a month. Are we sure that this pair don’t have kids?’

‘Or maybe a house-guest?’

Harvey returned home just after 1.00 p.m. He left the Toyota parked in the driveway. The RS 2000 stood in the open garage, apparently unpacked. Ten minutes after Harvey’s arrival, Maggie drove quietly up the slope and parked her car in its original position. She checked to ensure that no one was watching, before slipping back into the Transit.

McGuire handed her two large rolls, packed with tomato, lettuce and salami.

‘Thanks, Mario.’ She examined the filling. ‘Is this your Italian side coming out?’

‘Course not! The McGuires of Kilkenny were the salami eaters. The Corrieris of Milano were far too keen on their fresh breath to touch stuff like that. Their tastes lay in other areas!’ He flashed her a caricature of a lecherous grin.

‘You should be so lucky, constable!’

‘Yes, Sergeant, but you’ll have to contain yourself. Look. Our birds are flying!’

The double garage door was closing automatically. Harvey stood by the open hatchback of the Toyota, five Asda carrier-bags bulging in his hands. He lifted them with difficulty into the car, reached up on tip-toes and slammed the tailgate shut. Joy locked the front door and walked quickly out. She climbed into the driver’s seat. Her short fat husband clambered in on the passenger side. They saw a puff of exhaust smoke, then the white reversing lights came on and the sleek black car backed out of the driveway.

‘My car, Mario come on!’

‘Okay. Don’t forget the bloody rolls!’

The Toyota was clear of the cul-de-sac before Maggie had reversed out to follow it. She was three hundred yards behind when she saw it swing left, and circle the roundabout at the foot of the hill to join the A80, heading towards Stirling.

She tailed them, still at a safe distance, as the A80 became the M80, then watched half-a-mile later as the Toyota veered left to join the M876. Joy maintained a steady eighty-five miles per hour.

‘Christ,’ said McGuire, ‘if she puts her foot down in that beast, it’s goodbye to us.’

‘Don’t you believe it, cowboy, this wee thing can go too. Anyway, if the worst comes to the worst, we can phone in and have them stopped for speeding.’

Maggie drove skilfully, matching the Toyota’s speed. She kept other vehicles between her and her quarry, but always stayed close enough to observe the options taken at junctions. Eventually the M876 merged with the Edinburgh-bound M9.

‘Where do you think we’re going?’ McGuire asked.

‘God knows. Could be the bloody football. Is it Hearts or Hibs at home today?’

‘Oh, aye, and was that their half-time piece that Harvey loaded into the boot? Anyway, I hardly see the wee man as a rabid Hibs fan? No, it could be they’re heading for the Bridge. Will I call in?’

Maggie nodded and handed him the car-phone. He punched in Martin’s home number. A girl’s voice answered.

‘Hello, miss. Is Chief Inspector Martin in?’

‘He’s shaving. Hold on, I’ll call him. Andy!’ A second later she came back on the line. ‘Sorry, who’s that?’ McGuire introduced himself. ‘It’s DC McGuire,’ she called. ‘Sounds as if he’s travelling.’

A few seconds later Martin came to the telephone. ‘Hi, Mario. What’s up?’ McGuire explained. And as he did so his earlier guess was proved right. The Toyota headed for the Forth Road Bridge. Maggie followed tucked behind a maroon Sierra, from which a green and white football scarf trailed.

‘One other thing, sir. Joy bought a hell of a load of groceries this morning, and they loaded more than half of them into the car before they left.’

‘Okay, Mario, that’s good work. Call when you get where you’re going. I’ll wait here for you.’ His tone changed as he spoke away from the phone. ‘Sorry, Janie. Can’t be helped.’

Then he was back. ‘I’ll call Brian Mackie and tell him that the caravan’s on the move. Tell Maggie not to let them twig her.’

‘Would you like to tell her yourself, sir?’

Martin laughed. ‘No, maybe not. Good luck.’ He hung up and checked Mackie’s home number. The DI took some time to answer the call. When he did so he sounded as if he was rubbing the sleep from his voice. But he snapped awake quickly as Martin explained.

‘Stay by your phone, Brian, until we can establish where they’re going. Call your mate and have him ready in case you have to move fast. And when you do head out, make sure you have a full tank. You’ll be heading north, but at the moment it could be anywhere.’

There was no answer from Stockbridge when he called Skinner. He dialled Gullane, and Sarah answered. Bob, she said, had gone for a short-notice round of golf. Martin told her what had happened.

‘I’ll call the boss when they arrive wherever they’re going. Pending further instructions, I’ll do no more than maintain the surveillance. So long.’

He put the telephone back in its cradle and turned back to Janie. ‘Might as well put on a record. We could be here for a while.’