When she reached the bottom of the stairs, she bolted across the atrium – getting a few surprised looks as she did so – and made her way once again down into the basement.

She sprinted along the dingy corridors, panting hard with the exertion.

And then she was at the laundry.

She halted outside the door, trying to catch her breath while she peered in through the small glass window.

It was full of inmates working, pushing laundry trolleys, loading and unloading the washing machines and dryers, folding linen. She noticed a prison officer standing on one side of the room conversing with one of the inmates.

Bailey cursed to herself. She couldn’t just go in and start poking around. But she needed to know the specifics of the breach. To know that it was in the laundry wasn’t good enough. She needed to know exactly what form it took if Frank was to have a solid basis on which to launch a police operation and liaise with the prison authorities to lock down the prison.

She looked at her watch. Twelve minutes left.

She stood outside the door of the laundry, gnawing her lip and tapping her foot, trying to work out what to do, trying to work out what form the breach could possibly take. It was something in the fabric of the prison. Something which had been overlooked.

She stared at the big heavy door in front of her. The metal plaque riveted just beneath the window panel looked like it had been there since the prison was built.

‘WATER SUPPLY ROOM’.

These days, the water was piped in from the reservoir. That’s what Maggie had told her.

But back in the old days…

…The prison used to draw its water directly from a subterranean tributary of the River Foxbrook.

But the river had dried up when the reservoir was built.

Drawn directly…

…from a subterranean tributary…

…which was all dried up…

…which must lead out to a dry river bed somewhere to the north of the prison.

Source well concealed in prison.

And then it hit her.

The source was a well which was concealed in the prison.

A well.

The breach was a well. The well had drawn water from the subterranean river, but it had fallen into disuse when that had dried up. And the well was in the laundry – the ‘Water Supply Room’.

Alice had been telling them exactly that in not-so-plain English. The answer had been there right in front of them all along.

She had gone to the laundry that day to try and locate the well and confirm its existence. But it hadn’t been Terry who’d climbed out of it carrying drugs. It had been the killer.

It all fell into place now in a white-hot rush of revelation.

Bailey prayed it was enough to go on. It had better be. She had no choice now. She had no time left. She ran back along the corridor and up the stairs, heading for the phones. She still had time to call Frank.