A flare, spurting out from Mars - bright green, drawing a green mist behind it - a beautiful, but somehow disturbing sight.

221B BAKER STREET

"You were saying?" Molly demanded, her panic and fear momentarily forgotten.

Sherlock didn't say anything for a full minute, his drug-addled brain attempting to come to grips with the bizarre turn of events.

It was only when a Fighting Machine paused out the front of 221B that saw him snap out of it and into action.

"We're going," he said, grabbing her hand in one of his own, his belstaff in the other before charging out the door and down the stairs.

As they reached the bottom step, Sherlock called out "Mrs Hudson!"

"Quietly Sherlock," Molly hissed. "They'll hear you." But something glowed warm within Molly at the knowledge that despite being still drug affected Sherlock would still consider the welfare of his elderly landlady.

When Sherlock made to check Mrs Hudson's flat Molly pulled him towards the front door.

"She's safe Sherlock," she assured him. "She's with John and Mary."

Sherlock felt like a weight had been lifted from his shoulders. Now the only one's safety he had to consider were Molly's and his own.

He opened the front door as quietly as he could and scanned the area. The Martian that had been stationed outside had decided to move on and was currently lumbering down the street.

Not seeing any others in the vicinity, Sherlock decided now was as good a time as any to make their escape. He led Molly around the corner, pausing when they came to a manhole. Out of a pocket of the raincoat he produced a short crowbar that he used to force the latch so that he could raise the manhole lid. He then stepped back, indicating for Molly to make her way down first.

Molly cautiously made her way down. It was very dark and once Sherlock closed the lid they were going to be in complete darkness.

And Molly really hated the dark.

But as soon as Sherlock shut the lid he turned on a torch that he always kept in his coat pocket.

THE UNDERGROUND TUNNELS

When they'd both reached the bottom, Molly looked around in the limited light offered by the torch.

She didn't get much of a chance to ascertain anything of relevance about their surroundings. As soon as Sherlock had put his belstaff on, he made his way confidently down the darkened tunnels. Striding along he called over his shoulder. "This way Molly. Do keep up."

"Sherlock," she gasped as she caught up with him. "Where are we?'

He huffed impatiently. "Isn't it obvious?"

Molly could just make out the trickle of water as they moved along. "We're in a drain," she finally concluded, before muttering under her breath. "This better not be a sewage drain."

Sherlock turned and offered her a small smile. "London is a city from above and below," he explained. "The above you know. The one underground is a labyrinth of inter-connected tunnels that criss-cross the same area as above." He became more animated as he continued. "These tunnels are fascinating, they have their own history, being made up over hundreds of years as man has acquired knowledge and an ability to improve conditions for themselves. You may not realise it Molly, but we are wandering through one of the most industrious areas of London, all of it completely out of sight."

"Industry? Water and sewage drains," Molly said with obvious distaste.

Sherlock shrugged. "It all has to go somewhere. Better down here than through the streets."

They carried on in silence for a while, Sherlock in the lead as he turned down side tunnels like he was taking a walk through the streets of London.

Molly concentrated on keeping him in sight as she did her best to keep up with him.

When Sherlock pulled out his mobile from the inside pocket of his coat, Molly increased her pace until she was alongside him.

"Don't," she said. Stopping him as he was about to turn it on. "You'll want to conserve the battery for as long as possible."

Sherlock frowned at her. "I'll just recharge it later."

"You can't."

"Why? Was there a law passed banning the use of mobiles when the Martians invaded?" he sniped sarcastically.

"In a manner of speaking," Molly replied, her tone serious.

Sherlock said nothing, but waited. It was only now just dawning on him how much he was unaware of while he'd been high. He had a lot to catch up on in the short period of time before they reached their destination. He knew he was going to need to pay very close attention to every bit of information that was currently known about this threat that he'd only just become aware of. A threat like none he'd ever been confronted with before.

Realising that for now at least she wasn't going to be interrupted, Molly continued her explanation. "When the invasion happened five days ago, it took the authorities by surprise. When the Martians came to Earth, they were mistaken for falling stars. It was only when they emerged from their spacecraft that their intentions and capabilities were realised."

"How many ships have landed exactly?" Sherlock asked.

"Actual numbers are still unclear. But it has been confirmed that they landed in Horsell Common, Addleston and Pyrford. When they emerged they were in those huge machines, like that one you just saw outside Baker Street."

"Was no attempt made to communicate with these… Martians?" Sherlock was no diplomat, but he knew what standard protocols required in a situation such as this.

"Of course," Molly said. "But the Martians response was to completely obliterate those that were offering the hand of friendship."

"How?" Sherlock asked, becoming more and more intrigued.

"They produced some sort of funnel that they used to direct a beam of intense heat, a heat ray… There was nothing left…"

"What happened next?" Sherlock asked, directing Molly away from her distressing thoughts, although he was pretty certain he knew what her answer was going to be.

"The military responded in kind," Molly confirmed. "They were successful in bringing down two of the machines."

"I assume the Martians weren't expecting a fight," Sherlock postulated.

"No, I don't think they thought we were capable of taking them on," Molly responded. "Once they realised their mistake they instantly set about ensuring their superiority."

"So they took out all power, telecommunications and military installations."

Molly nodded. "We have effectively stepped back in time. Our technology, such as it is, is the equivalent of that in the late 1890's."

"Their strategy makes sense," Sherlock noted. "Reduce us down to a point where we are no longer a threat," he paused a moment, deep in thought. "A pity the military chose to show their hand so early," he murmured. "That was careless."

"They didn't have a choice," Molly said defensively becoming slightly annoyed by Sherlock's attitude. Though she couldn't fault his logic.

Sherlock had moved ahead of her again. From where she stood she could see he was searching for something.

"Ah, here we are," Sherlock cried triumphantly as he began to ascend a ladder.

"Where?" Molly asked, following him up.

"To the most secure building in the whole of London," he replied as he reached the top and began trying to push the trapdoor open.

"So, Buckingham Palace? The Houses of Parliament? Number 10 Downing Street?"

"Nope," Sherlock said as he finally got the door open. "They have nothing on this place."

As he emerged into the room, his eyes landed on a pair of highly polished, expensive leather shoes and the tip of an umbrella.

"Brother dear, so good of you to join us."