Swithering which to answer first, she chose McNab, already feeling guilty at it not being Chrissy.

‘Where are you?’ he demanded on pick-up.

‘On my way back to the lab.’

‘Don’t go there. You’re needed at . . .’ The address he gave her was the street Mary McIntyre had disappeared from.

‘Why am I going there?’

‘It’s Alec McLaughlin. He’s been found dead in suspicious circumstances. Chrissy is on her way.’

Before he could ring off, Rhona told him about her find in the loft of Rowan Cottage.

‘I checked that box,’ he said. ‘In case the diary was in there. You think the jumper’s part of Mary’s missing clothes?’

‘We can test for her DNA, but it’s wool and blue and the right size,’ Rhona told him.

‘If it is Mary’s, then Karen Marshall’s had it since the day Mary disappeared.’

He didn’t say it, but Rhona could hear the words anyway. Karen Marshall had secrets to tell.

Rejoining the motorway, Rhona edged her way past Glasgow city centre and headed south, using the satnav to direct her to the address McNab had supplied her with.

Eventually she found herself driving up a steep brae she recognized from an earlier Google image, passing a mix of local authority houses and those that looked as though they’d been purchased, probably during the Thatcher era.

To her right, the open ground sketched out in DI McCreadie’s notebook was no longer wild, but tamed with close-cut grass and budding yellow and purple spring crocuses. Some of the gardens opposite had become parking places for cars, including number ninety-five, Karen Marshall’s old home. Almost directly opposite the house was the drive that led into the Catholic school which her pal Mary had attended.

Rhona halted there for a moment, taking in the scene she’d so far only viewed as a police sketch made forty-five years ago, or as it was now via Google Earth.

On the far side of the school drive was a steep bank, topped by an area of waste ground, not yet cultivated by the council. North of this, on the crest of the hill, Rhona could make out the playground and buildings of the Protestant school. Finally, to the east, the dark shadow of the trees, where the girls had built their den.

Two doors up from Karen’s former home had been Mary McIntyre’s house, and was, according to McNab, where her older sister, Jean, and her husband, Samuel Barclay, now lived. Here the garden had been well maintained, and it too was bright with spring bulbs.

As she crested the hill, police vehicles appeared in a line in front of a house with a dilapidated air and boarded-up windows, the patch of garden in front home to a discarded mattress and other assorted junk.

According to McNab, McLaughlin’s body had been discovered in his teenage home, although he’d been residing in a Glasgow hostel for the homeless after his release from Barlinnie.

So what had brought him back here?