For a moment, Cooper thought he was going to lose control. He felt as though he might let all the stress out in a burst of anger against the wrong person.

‘Look, just give me a minute, Georgi.’

Just below the car park, he found a pond. It lay in a circular hollow near the road, overhung by bay trees. In the middle of the water, a fountain sprayed over a column of tufa. Dozens of the black beetles called waterboatmen sculled on the surface among floating lilies, perhaps fooled by the strings of coloured lights into thinking it was still daytime. In fact, the column looked to be more moss than tufa. But on the bank behind it were patches already turning to stone. The vegetation looked normal from a distance, except for its colour. But it was already dead and hard, retaining only the appearance of life.

‘It looks as though the gardens are being opened up,’ said Fry through his ear piece. ‘The crowds are starting to move that way.’

‘Well, at least they’ll all be in one place. There are thousands of them. And they’re still coming in. There’s another busload arriving now.’

‘I’ve asked for a car to cruise through the rugby ground to see if they can spot Mullen’s car at the park-and-ride.’

‘Good idea.’

Kotsev was waiting for him on the pavement. Most of the police officers deployed in Matlock Bath tonight were on traffic duty, keeping the lines of cars moving. Across the road, the gardens themselves were being patrolled by security staff and stewards in yellow jackets. As soon as the fairground and fast-food stalls had set up, the barriers were taken down and people began to filter past the volunteers standing by with buckets for donations.

‘There are so many people,’ said Cooper. ‘We’d better split up from here. You know what Brian Mullen looks like, Georgi?’

‘I have the photograph. And there’s the child with him –’

‘Yes, probably.’

Cooper worked his way past the St John Ambulance, the Venetian Boat Builders Association, stalls for the Cats Protection League and a Chernobyl children’s charity. A woman who looked like a gypsy pulled a scarf across her face and turned away from the light. A fortune teller, or perhaps a pickpocket. Well, it wasn’t his business tonight.

It was dark now, and all the children were carrying rainbow spinners, yellow light sticks or flashing fish. One by one, they stopped and pointed at the illuminated butterflies and dragons in the trees. Cooper came to a central area lined with fast-food vans. The local radio station, Peak FM, had set up its roadshow in the bandstand, where an ageing Elvis in a black outfit was belting out songs from a cloud of green artificial smoke.