Danny ran his hand along the smooth surface. “Could obsidian be this smooth, naturally?” he wondered.

“Absolutely. Polished obsidian was even used for mirrors thousands of years ago. I would expect a substance such as obsidian to be that smooth naturally. Danny, can you show me a more ground level view, please, from the edge of the stone across it?”

He obliged, climbing down the side of the stone that Captain Montreaux had just emerged from. He scanned the edge of the stone, and then raised his head slightly and tilted it down so that Jane would be able to appreciate how flat and rectangular it was.

“Fascinating,” she said eventually. “It looks perfectly flat, and the stills I have taken from the video feed suggest that the angled edges I have seen are all at ninety degrees.”

“What do you make of the grooves, Dr Richardson? Could they have been carved or etched into the surface?” Montreaux asked.

“No,” she replied. “At least not if the stone is indeed obsidian. Obsidian is very similar to flint, in that it splinters and creates flakes. Fantastic for making arrow heads and knives, but very difficult to craft, and virtually impossible to chisel or strike with any reliability. When used in ornaments nowadays, it is usually polished, so it’s relatively easy to create a smooth and accurate edge. However, a groove is entirely different: I don’t think you could polish a groove into a flat piece of stone, at least not a groove like that.”

“Can’t you use lasers?” Danny offered.

“Indeed you can. In fact the only useful application of obsidian I can think of right now is surgical knives. The blades of precision instruments can be fashioned using a laser. Because of the compact nature of the crystals that make up the rock, the width of obsidian blades can literally be measured in molecules, so they are hundreds of times more accurate than steel.”

“Stone knives?” Montreaux was amazed.

“Even now they’re still used in heart surgery, Yves,” she confirmed.

Montreaux took a step back and contemplated the stone beneath him. He found his eyes inexorably drawn towards the crater wall by the grooves. He wanted nothing more than an excuse to start digging like crazy, but if this was what he sensed it to be, then things would have to be done properly.  “Dr Richardson?”

“Yes?”

He measured his words carefully, not wanting her to infer anything unprofessional. “Having seen the stone we are standing on, its dimensions, shape and,” he paused, as if looking for the correct terminology, “other characteristics, what do you think made it?”

“I am not a geologist by trade, Captain,” she replied without hesitation. “However, I have seen some incredibly unbelievable rock formations on Earth, particularly where cooling magma is involved. The grooves may have been set as the magma cooled, possibly the imprint of other stones, maybe even by water, which we know at some time existed in abundance in this area. This stone could be a naturally occurring phenomenon. I would need to see a sample.” She waited for a response, but none came. “And I would very much like to visit the stone myself,” she added.

Danny looked at Montreaux and winked. “Jane, cut the bullshit now, OK? We’ll use that last bit as a sound-bite for Earth, you sounded great,” he said. “Now tell us what you really think.”

“Danny, you are standing on a perfectly flat surface, as smooth as a pane of glass, with perfect parallel sides and straight edges, all seemingly at a perfect ninety degrees to each other,” she said. “Not only is the stone flat, it also appears to be horizontal, which is why you two aren’t slipping off it. It’s also jutting straight out of the side of the crater, possibly pointing directly to the centre of said crater. And to top it all off, there is a groove in its surface that is not only aligned with the stone itself, but is also uniformly one-point-eight centimetres deep and ten-point-six centimetres wide – I know because I’ve checked it from the video feeds you sent.  Can any one of these features on their own be produced in the natural world? On Earth, certainly. On Mars? Who knows, but the laws of physics are no different here to back home, we simply have different environmental conditions. I would say that probably yes, too. Now you’re left with the big question.” She paused. “Is it possible for all of these features to be found together, in the same place, given the context of the stone?”

“Dr Richardson, I appreciate your thorough summation of the situation, but could you just give us a straight answer?” Captain Montreaux was getting uncharacteristically impatient. He knew what the answer was, he just wanted to hear her say it.

“Yves, I am a scientist, and we never say things of any major significance in anything less than five hundred words. But to be blunt, there is no doubt in my mind that what you are standing on was put there. And although I cannot believe I am even saying this, I am sure that you and Danny are not the first beings to have stood on it, either.”

There was a very long, weighted silence.

Captain Montreaux couldn’t help but remember the journey to Mars, the conversation with Lieutenant Su Ning, the suspicious circumstances of her death.  He had known then that something big was going on, and things certainly didn’t get any bigger than this. On the one hand he was excited at the magnitude of their discovery, but on the other he knew that people were prepared to kill them to cover it up. His heart sank. He knew deep down that nobody back on Earth of any importance to him would ever find out about their discovery. He also now knew why they had landed on the northern edge of the Hellas Basin rather than any other, and why the pre-planned coordinates of their rover expeditions had been so exact. And now that they had found the Jetty, what next?

If this is going to be part of a cover up, he thought, how likely is it we’ll be allowed to return home alive?

“What do we do now?” Danny broke the silence.

Montreaux looked over at him, hoping that the reinforced Plexiglas of his helmet did not reveal anything. “I have an hour of air left in this cylinder, how about you?”

“About the same. And we have three hours more in Herbie.”

“Dr Richardson,” Montreaux hailed her.

“Yes?”

Through the environmental interference on the com system, Montreaux fancied he could detect something odd in her tone, a hint of self-assuredness, of knowing, and suddenly an alarming thought materialised: was she in on it? Were they both? The dark thoughts crystallised, only making sense now, as he stood on the alien stone with the enormity of the situation staring him right in the face. Did either of them know of the cover-up because they were involved? He had a momentary flashback of Dr Richardson and Captain Marchenko the previous day, having one of their friendly arguments. As they did every day, he thought. He swallowed hard. Was he the only one not in on the cover-up? Was he going to be next?

“Captain?”

Danny’s voice came through faintly in his earpiece. He cocked his head and looked at the Russian. Suddenly extremely self-conscious, he realised that he must have been looking into space for quite some time.

“Yves, are you alright?” Jane sounded genuinely concerned.

He snapped out of his daydream in an instant. Nonsensical paranoid delusions, he concluded.

“Dr Richardson, you’d better put a hold on those steaks, for an hour or so.” He gestured towards the wall of the crater, to where the groove in the stone disappeared. “Captain Marchenko, let’s get some tools from Herbie and find out where this groove goes.”

From its viewpoint two thousand metres further along the edge of the Hellas Basin impact crater, Beagle watched the two figures ascend the crater wall.  Using a high-resolution lens, it zoomed in on the black object, three hundred metres below, upon which they had been standing moments earlier.