Doyle took the envelope and letter to forensics and paced up and down like an expectant father until Malcolm pronounced. Nothing extraordinary in the paper or the handwriting. Some prints had been lifted from the note and it was up to Doyle to feed that through the computer. Malcolm had found two hairs in the envelope and he would put that under the microscope. Doyle felt he was on firmer ground with the prints, and so it proved.

Doyle burst into the filing room where Bodie and Murphy were turning over files. "Bingo!" he announced. His colleagues looked up expectantly. "The finger-prints on the letter belong to George Collings."

"George Collings," Murphy repeated as he lept up to get out a file he knew to be there.

Once that was secured under his arm, the three men got in the car as Murph read out the headlines. Gangster, let out of jail on licence two weeks ago. Present address unknown. Doyle was heading north.

"Where are we going?" Bodie asked, hanging onto the door handle as Doyle got the car up to 60mph.

"Collings' mob have a barge and a warehouse at Wapping. The cops raid it occasionally, but Collings is usually one step ahead of them – even when he's in jail. But not this time. This is surprise time."

His colleagues checked their guns and ammo. Doyle silently passed his gun to Bodie who rummaged in the glove compartment for spare ammo. He passed the weapon back as Doyle pulled in quietly onto some wasteland. They would be on foot from here and following Doyle's lead. Their hackles were raised and anger on their boss's behalf crackled between them. Shortly, the warehouses loomed ahead of them in the darkness. Their progress became slower and more furtive. No words had passed between them since they left their car. They were in tune with each other, literally following in each other's footsteps.

Doyle pointed with his gun towards a gap between two buildings. His colleagues followed without question. They crept alongside the vast warehouse until they saw huge sliding doors which would lead into the building. Doyle indicated that they fan out. They saw no vehicles in the vicinity; no-one was at home. Cowley had drilled into them not to jump to conclusions, so they remained on alert. They met up eventually by the water's edge. They could hear the lapping of the river as the tide rose steadily under a half-moon. Doyle slipped down the landing steps as far as he could; his colleagues crouched by the edge, watching anxiously. Doyle got out his small torch and shone it along the bank. It picked out the slime and detritus of the river, but nothing further. He reluctantly returned, shaking his head at his colleagues. They sighed in frustration as the next two landing steps also drew a blank. They hunkered behind some barrels for a brief confab, the cold wind seeping into their light clothing.

"What now, Ray?" Bodie whispered. His partner could hear the frustration, yearning for his friend to come up with something. He felt that he, himself, should be offering something but Doyle seemed to know more about this bloody Collings than either he or Murph. Doyle stared unseeingly into the darkness. His friends knew not to interrupt his train of thought as they shivered, hugging their jackets closer to their bodies. Eventually Doyle shook his head and ran his hands through his curls – a tic which Bodie knew well. Something was gnawing at the edge of Doyle's consciousness just out of reach.

"Something, something," he murmured. Not being able to snatch at the ghost, he suggested heading back to the car. Perhaps a rereading of the files which Murphy had brought along may jog his memory. He was bitterly disappointed with himself. He got up stiffly and looked into the expectant eyes of his friends. "Sorry. I just can't get it this time. Perhaps those files …"

"Give it time, Ray," Bodie soothed as they headed back, stretching an arm over his friend's hunched shoulders.

But they knew that Cowley hadn't got time. The tide was rising and, if he was still in his pyjamas, he'd be getting hypothermia by now. Doyle stopped suddenly, which had his pals reaching instinctively for their guns.

"The cavern!" Doyle said in a 'eureka' moment.

His comrades had no idea what he was talking about but headed back with him. Ray had eagerness in his step and his friends had a job to keep up with him without falling over something. They returned back to the warehouse and this time they crept inside. They were on high alert and stood quietly for a few moments to get their bearings. The only sound was the skittering of rats and the rattle of the timber against the rising wind. Doyle seemed to know where he was going. They kept to the shadows until they got halfway in when Doyle stopped. He raised his gun for stillness. His friends were statues. Doyle hunkered down and seemed to be looking for something. He risked using his torch again. Footprints. There were footprints in the dust of ages. Doyle looked up at his friends as a smile slid across his face. His pals grinned in return. It may not be much – it may not mean anything at all – but it was a spoor to be followed – and they did. There were three sets of footprints – two of boots and one barefoot set. It had to be Cowley's. They traced it to a hatch in the wooden floor. The pair eased it up slowly as Murphy acted as lookout. They still tried to be as quiet as possible. Doyle shone his torch into the darkness. The stench of the river met their noses and the loud lap of the water could be heard.

"Sir? Mr Cowley?" Doyle whispered, now on his belly as he peered down.

"Doyle?"

The voice was weak, but the men could have yelled with joy and relief.

"We're here sir. Are you tied?"

"Well of course I'm tied. I'm not here for the joy of the river!"

Yes, Cowley was in fine form! Grinning, Doyle eased himself down the ladder as Bodie played the torch and Murphy continued as sentinel. Doyle got his Swiss army knife out of his back pocket and he sawed carefully at the thick ropes which bound his boss to the iron brackets. The water was up to his waist. Doyle awkwardly hauled his boss up and Bodie reached down to take the load. Immediately the Cow was 'landed', his men took off their jackets to warm him and Murphy offered his shoes and socks. Bodie gave Murph a piggy-back and Cowley, encouraged (as Bodie hoped), allowed Doyle to give him a ride too to the car.

Bodie took the wheel and soon had them back on the road to the hospital. Murphy, sat next to him, radioed in their position, to the delight of the night watchman. Doyle, meanwhile, massaged Cowley's limbs and tried to keep him awake until they arrived at the hospital. They were met by anxious doctors who soon had him on a stretcher wrapped in thermal blankets.

It was an anxious few days before Cowley turned a corner and returned to the waking world. He had been guarded day and night by his agents, after a ranting lecture by their deputy boss about being kept in the dark. CI5 weren't going to let the Cow disappear again. But Bodie still gnawed quietly at the 'Annie problem', but he would keep that little quandary to himself till he found an answer.