The sergeant checked their BAR, but they were so shallow that they both had plenty to complete the dive. Ghostly images came into view and Kelly wondered what attracted people to this particular job; she thought it grim, like being a miner, stuck in the airless dark.

The radio crackled again, and one of the divers reported that her metal detector was indicating something solid beneath her: it was a small object, the sergeant explained, judging by the sound of the alarm and the way the diver cast it across the area. She was instructed to search beneath the mud carefully. They watched as she tentatively sank her hand into the mud and probed, as if caressing a pet.

Kelly held her breath and squinted at the screen. The diver pulled something from the dirt and it kept coming. When the detritus settled, they could see that she was holding a knife.

‘Yes!’ Will fist-bumped the air.

‘Submerged in no more than two centimetres of dirt, Sarge,’ the diver reported. ‘Looks like a recent dump: no corrosive damage and no adherence of organic matter. It’s pristine.’

At the same time, the other diver’s metal detector indicated another find. The same procedure was followed and the diver put his hand in where the detector was most acute. After a few minutes of gently delving, he pulled an object from the gloop. It was a second knife.

Will and Kelly looked at one another and slapped high-fives.

The atmosphere in the van was super-charged. Kelly knew that any team helping the police in a professional capacity wanted results, and they’d hit the jackpot.

‘Shall I halt the dive?’ the sergeant asked.

‘I think we’ve found everything we’re going to.’

‘Right you are. Good job, guys, bringing you back in.’

They watched as the divers gave the OK sign and turned around. It was a short swim to shore and there was no need for off-gassing, as they weren’t deep enough. They sat on a platform at the edge of the pond and took off their tanks and buoyancy aids, and Kelly and Will went outside to congratulate and thank them. They wore full suits because the pond was freezing and the amount of bacteria probably eye-watering, but they removed their gloves and shook hands.

The items had been carefully stowed in strongboxes, and they were handed over to Will, who took them to the van. Advances in latent fingerprint extraction on items submerged in fresh water had rocketed forward in the last ten years, to an extent where defence barristers had been rendered red-faced in court: the science staggered everyone.

They had something. They had more than something. The knives were different sizes and she’d know soon enough from Ted if they were a match. Now she had to get them measured, logged and sent over to him.