The filling station had run out of diesel at around seven-thirty at night. A customer had been filling the tank of his SUV when it had run dry after just a few litres. Just seconds earlier, the indicators had flashed a low-level warning. Mr Patel, the station's owner, had thought it was an error, given that the bunkers had just been filled that morning. If a member of his staff had been on duty at the time he'd have thought he'd been duped – conned out of a delivery. But the gauges had indicated that his tanks had been filled with the same amount of diesel and petrol he'd signed for.

This had left only one possibility, and it filled him with dread. Unfortunately, the seriousness of the incident had meant the involvement of the fire brigade because the only rational explanation was that the diesel bunker had suffered a catastrophic failure. If that were the case, his insurer was going to face a hefty bill. It wasn't just the repair of the structural damage – there was the clean-up bill to consider. The surrounding ground would be contaminated, and would probably need digging out. He'd be out of business for months, at least. If it had leaked into the sewers then there was the potential for a massive explosion.

It was now ten o'clock, and he was standing on the other side of the police cordon watching the fire crew flush the drains with industrial detergent to reduce the fire risk. He was thankful that he wasn't in a residential area, and that he didn't have a couple of hundred displaced households pouring their ire on him. All he could do was watch the figures on the forecourt and wait for any news.

 

A police patrol car pulled up onto the forecourt and a sergeant got out. "Alright, Hughesie?" said Steve. "Makes a change, eh? No one hurt. No motors."

"I was going to ask how long you're going to be," said Sergeant Hughes. "We've got a hell of a big diversion."

"Just about to take a look inside. Got a specialist coming in from Tilbury for a butcher's. Refinery fire officer. Private, so we'll have to charge him out of budget."

"I suppose you don't get many of these."

"Serious business, ruptured fuel bunker. Think back to the Buncefield explosion in 2005. The petrol one seems to be intact, but there's always the danger it'll go. Diesel ain't quite so bad, but petrol – whoof!"

"What caused it?"

"Search me. Happened very fast from what I hear. You'd expect a slow leak – a crack, something like that. This is pretty new, too. Mr Patel over there said it's no more than four years old. So if one bunker's failed suddenly then you have to think in terms of something big like subsidence. But the thing is that the concrete's reinforced, and a good six inches thick. Enough to stand on its own. You could take one of these out and crash a car into it, I should think. We don't get earthquakes here, but they're designed to withstand them."

A couple of firemen wearing breathing apparatus lifted off the inspection hatch.

"Right, here we go," said Steve. He put on his breathing equipment and walked forward twenty feet to join the other two men. He lowered himself onto the concrete beside the inspection hatch. One of his men handed him a heavy duty flashlight. He put it into the tank and leaned his head inside. He let out a muffled yell and dropped the light. There was an echoing bang as it hit the bottom of the tank, and a scuffling noise from inside. Steve jumped to his feet and ripped off his mask.

"Get back!" he yelled. From inside the tank came the unmistakable sound of masonry hitting concrete, then something that sounded like earth being thrown onto the floor of the chamber. All four men froze, listening to the sounds. After a few seconds, there was silence.

"What was that?" asked Sergeant Hughes.

"No idea," said Steve, shaking. "I could swear there was..." He shook himself. "Let's take another look. Roy, you want to have a butcher's too?" He took another torch, and he and Roy crept forward to the inspection hatch. Steve poked his head cautiously over the side of the hatch and flashed the torch around, keeping his hand at ground level. He then put his head into the hole, reached in and shone the light around. He pulled his head back out and indicated to his colleague to do the same. Hughes couldn't hear what they were saying.

They got back to their feet and pulled off their breathing apparatus just as a private car rolled to a halt on the forecourt. The driver got out. He was a portly man in his fifties wearing jeans and a casual shirt, looking all the more haggard for having been called in from home.

"Evening," he said. "Steve Jones? Dave Lore. The two men shook hands. "You're one of Parkie's boys, ain't you? How is the old dog? We were on blue shift together back in Basildon."

"Ah," Steve brightened. "Yeah, Dave Lore. Parkie's doing alright. Close to retirement now, of course."

"Yeah, I got out eight years ago. Sit on me arse in an office now. Risk-assessment and contingency planning mostly. What's the bother here?"

"Need your advice. More your thing, mate. Leaking tanks and that."

"Cleared the drains, I see," said Dave, thumbing back towards the firemen who were finishing up with the detergent.

"Owner says there's pretty much a whole tankful gone into the surrounding area," said Steve. "Catastrophic failure. Now, I was expecting a fracture and a slow drain."

"Most likely scenario, yes. Not likely it's just sprung a leak." Dave looked around. "Especially not with building regs the way they were when this was built."

"Right, if you wouldn't mind doing the honours, then. Tell me I'm not imagining things."

Dave pulled on a protective suit, and was given breathing apparatus and a flashlight. He accompanied Steve up to the hatch and looked in. There was a muffled exclamation and Steve lay down on the ground next to him. There was an animated discussion, which was unintelligible from where Hughes and Roy were standing.

"Doesn't make sense," said Roy to Hughes.

"How?"

"It's six-inch thick steel-reinforced concrete, right?"

"Yes."

"Well, it looks like something's actually... I dunno how to describe it. Something's punched in to the tank."

"Punched in?"

"Yeah, the reinforced steel has been cut and bent inwards."

"You mean cut?"

"Clean edges."

"Just like if you'd had some of those big pincers? Just like the fuel tank of that taxi the other day?" Roy looked at him. He nodded.

Steve and Dave came back to join the other two men.

"What's the verdict, gents?" asked Hughes. "Can I reopen this side of the carriageway?"

Dave and Steve looked at each other. Steve nudged Dave. "You're the expert mate. And you're getting fees for this."

"There's nothing inherently wrong with the structure," said Dave. "So the remaining tanks are safe in themselves."

"Okay," said Hughes.

"And the diesel has drained away. And I mean really drained away. Effectively. Deep. Very deep. That's why Steve's lads didn't find any contamination in the drains."

"So what happened?" asked Hughes.

"Well," said Steve, "we reckon this is one for the Old Bill. It's been half-inched, hasn't it?"

"What do you mean?"

"Someone's nicked the diesel. They've only driven something in there and nicked it, haven't they?"

"Get off, mate," said Hughes. He stared at Steve, and the fire officer smiled at him.

"Well, me and Dave reckon someone's crashed a drill-bit, or a pig from a pipeline into it."

"A pig?"

Steve looked at his feet. "Yeah, you get these motorised things that can go along old sewage, gas or water pipes. As they inch forwards they break the old pipe and push the fragments into the surrounding earth. They pull in fresh pipe behind them. Plastic stuff that's good for the next hundred years or so."

"I think I know the things you mean," said Hughes. "I saw the water people using one in a road a few years ago. About three feet long and maybe six inches wide?"

"Yeah, that's the job."

Hughes ordered his men to begin taking off the diversion. The filling station would remain shut until someone a couple of ranks above him could talk to one of Steve's superiors in the cold light of day and decide what to do. Dave Lore said his goodbyes – he'd be one of the experts consulted the following morning.

"Here, let's have a talk," said Hughes. "I can drop you back at the station."

"Sure, mate," said Steve. They walked to Hughes' patrol car and got in.

"What did you see when you first looked down there?"

"This big hole. The concrete had fallen into the tank. The steel reinforcing rods had been cut and bent inwards. I've never seen anything like it. I was stunned."

"Stunned enough to drop your torch?"

Steve looked back at him.

"Look, we've known each other – what – maybe fifteen years. Not exactly Christmas card list, but... you know, we're professionals." Steve nodded. "We've seen some bloody horrible messes out there," he thumbed in the direction of the dual carriageway. "But I've never seen you flinch." Steve nodded again. Sergeant Hughes cleared his throat. "I'm going to guess that the hole was about two metres across. Right?" Steve perked up. "I'm also going to guess that there was quite a bit of soil pushed back into that tank. Am I right?"

"How'd you know? Roy tell you?"

"No." Hughes took his camera out from the back seat and switched it on. "Have a look at these. I took them after everyone else left the other day."

"This is the taxi that crashed into another vehicle, right?"

"Yeah, the vehicle that didn't exist. Let's scroll through to the ones that didn't make it to my report. Here you go. This is what I saw in daylight. See? Big mound of earth. Then I saw these tracks leading down to it. Something heavy, maybe a couple of metres wide. Something pretty heavy, but the imprints aren't as regular as you'd expect from a big tractor tyre or a tracked vehicle."

"And this was right next to the crash scene?"

"The team did look for the mystery vehicle in the immediate vicinity, but there was nothing. Remember, we couldn't find any tyre marks – not even any glass that didn't belong to the cab. No way you could have seen it in the dark."

"Sure, I'm not saying your guys didn't do their job. I'm just wondering why you're showing me this."

"Steve, this happened about four miles from here. Right? Heavy enough to dent a black cab. Two metres across. Something that can apparently cut through reinforced steel. And all it leaves is a molehill. Did I mention the molehill smelled of diesel?"

"So what did you say in your report?"

"I didn't."

Steve said nothing.

"And I was going to ask you what you're going to put in your report."

"As I said, the only conclusion me and Dave could make was that something broke in. Had to be one of those pigs. Or maybe a drill bit from one of those fracking operations. The diesel would have just flowed off into the hole, wouldn't it?"

Hughes was silent for a moment. "There are no two-metre wide pipes around here. And I doubt very much a pig's going to be able to reverse with a dirty great pipe trailing behind it. Plus, I see no construction crews. As for a fracking drill –– be serious."

"What other explanation is there?"

"Steve, level with me." Hughes squeezed the fireman's shoulder. "I heard the noise. That wasn't a machine. I want to know what it was."

Steve turned to stare out of the passenger window for a few seconds, then looked Hughes in the eye. "This is between us, right?" Hughes nodded.

The fireman took a deep breath and then sighed. "It was black and shiny. Big thing. I only saw what I think was the back of it. And a couple of legs."

"Legs?"

"That's what they looked like."

"Go on. What did the rest of it look like?"

Steve paused before replying. "A cockroach. A beetle sort of thing. You know?"

Both men stared ahead through the windscreen at the passing traffic. It was Hughes who broke the silence. He picked up the camera and scrolled to the photos of the tracks. "A six-foot wide beetle would probably leave footprints like that, wouldn't it?"

"A big beetle that likes diesel. I'll let you file your report first – stealing fuel is a police matter."

"Nah, Steve. A six-foot wide beetle with a stomach full of diesel is a fire hazard."

The laughter of relief left them in fits for a couple of minutes.

"Look," said Steve, taking controlled breaths. "Dave's going to report it as a stray pig or a drill-bit from a fracking company. There'll be a search and it'll turn up nothing. That's none of our concern."

"Until someone gets killed. I was going to send these to a website I've heard about. They deal with reports about the paranormal from police officers. All anonymised. Usually it's UFOs and all that rubbish. It'll be a nice change from the usual content. Send me your pictures and I'll submit them at the same time. I can't just do nothing, can I?"

"You're right. Maybe someone reads that stuff. Maybe they can figure it out."