Harry, Ron, Hermione and Ginny did as they were told. They raised their hands in the universal sign of surrender, though they did so each with a matching expression of bottomless bewilderment.

This thing - which seconds earlier had crawled out of an old, cobweb-ridden, hidden passageway on Hogwarts' second floor - stomped towards them, and regarded each of them with a gaze so angered, so aggressive, anyone would assume you had known this creature all its life, and been incredibly horrible to it. When in fact, none of the four humans had ever set eyes upon this 'Sontaran', nor anything that resembled it.

"Are you deaf?" the Sontaran barked. "I said lay down your weapons!"

They shared a blinking, bemused glance.

"We don't have any weapons?" said Harry.

The little, blue-clad, potato-faced thing laughed.

"You think me a fool? A Sontaran never goes into battle without the advantage of knowledge. The humans in this corner of the planet use tiny, pathetic, wooden things, which expel feeble energy."

"…are you talking about wands?" asked Ron, genuinely unsure. "Is that a really long description of a wand?"

"I don't care what you call it! Just remove them from wherever they are holstered and toss them on the ground."

They hesitated for a second, but then the Sontaran jabbed his own weapon in their direction, and they felt the heat from the blue aura at the end of it. Reluctantly, they each took out their wands and let them fall to the floor.

"Now," said the Sontaran. "You will do as I say and then you will each be executed."

Harry frowned. "Don't you mean 'or you will be executed'?"

The Sontaran nodded. "That as well."

There was a pause as everyone tried to make sense of this.

"So we have to do what you say," said Ginny slowly, "or you'll kill us, and then even when we've done what you've asked, you're going to kill us anyway?"

"Correct."

There was more confused silence.

"It will be a glorious execution, worthy of a warrior," said the Sontaran. "If that provides any comfort."

"Not especially," Ron informed him.

"Regardless," the Sontaran continued, producing a piece of parchment and holding it up to Harry. "You will show me where the remains are, so that I may execute you and retrieve them myself."

Harry sighed in frustration. "I'm sorry, but you're not the first person to ask me about remains, and I really don't know what you're talking about so - hang on, where the hell did you get that?!"

It was only when he had seen something moving on the parchment being held out to him that he actually looked at it, and realised that it was no ordinary parchment at all. It was the Marauder's Map.

The Sontaran merely grinned, as though he took great pleasure in Harry's reaction. "The resources of the Sontaran Empire are vast. Nothing of yours is safe from us. So you would do well to save time and reveal your secrets!"

Ron looked at Harry in wonder. "How could you leave that lying around for anyone to just nick?"

"I didn't!" Harry cried.

"When was the last time you even used that thing?" asked Ginny.

"I don't know," Harry replied. "Not for years. As far as I knew it was safe in my wardrobe in… the cottage. Wait a second. Was that you? Did you break into my house and steal this?"

"Enough!" the Sontaran barked. "You will tell me where the remains are, or I shall kill one of your companions in front of you."

The Sontaran jerked his gun in the direction of Ron.

"Hey!" Harry yelled. "I swear, I don't know what remains you're talking about."

"Lying will not save your friend," the Sontaran yelled back.

"Don't!" Hermione cried, as both she and Ginny placed themselves protectively in front of Ron.

"I don't care which one of you I kill," said the Sontaran angrily, "so long as I find out what I want to know."

"I don't even know what you want to know!" said Harry.

The Sontaran growled and aimed his weapon. "Let's see if a corpse will loosen your tongue."

It was at this moment, with the Sontaran's stubby little finger on his trigger and ready to fire, that gravity momentarily suffered a glitch. At least that's what it felt like. There was the most thunderous sound imaginable, and suddenly everything was thrown. Harry's feet physically left the ground and then were furiously dropped back down, as the whole castle shook like it had been dealt a mammoth blow.

He may have even blacked out for a brief second, because the next thing he remembered was seeing a rusty metal faceplate staring back at him. He was on the floor, along with some of the suits of armour that had been lining the hallway and a few chunks of rock and debris from the ceiling.

"Everyone okay?" he asked in a strangled voice.

"Fine," Ginny groaned. "Sort of, anyway."

"Me too," came Hermione's weak response

"What the hell was that?" asked Ron

Harry didn't have an answer. He got to his feet, helping the others do the same, and his eyes fell upon the only person who was still on the floor. The Sontaran lay face down, with a large chunk of the ceiling resting on the back of it's neck.

"Couldn't happen to a nicer bloke," said Ron bitterly, as he retrieved their wands from the floor.

More loud noises, ones not quite so close, began to rumble from off in the distance, Ginny rushed towards the half-shattered window at the end of the hall.

"Harry…" she said. "You better come see this."

Harry ran to her side, but as he looked out across the darkness-covered school grounds and the flickering lights of Hogsmeade, he saw nothing out of the ordinary. Then Ginny softly reached forward and tilted his chin so that he was looking up.

"Oh."

"Do we even want to know?" asked Ron, still with Hermione next to the Sontaran.

"It's the lights," said Ginny, struggling to even find the words to describe what she and Harry were looking at. "But… they've gotten bigger. They're massive!"

Suddenly, Harry ran back up the hallway and grabbed Hermione by the shoulders.

"McGonagall's statue spell," he spluttered.

"What?" said Hermione.

"From the battle! When we first realised Voldemort was coming for Hogwarts, McGonagall cast a spell that made all the castle's statues come to life, but what spell was it?"

"I don't know," she said. "Hadn't Ron and I gone looking for the Chamber of Secrets by that point?"

"Why do you need to know?" asked Ron.

"Because we need to barricade Hogwarts again."

That shut everyone up for a second.

"We need to do what, now?" exclaimed Ron, as Hermione shrugged out of Harry's grasp on her shoulders and ran to the end of the hall to see what was still rendering Ginny frozen in place. The noise of repeated explosions was still coming from somewhere out of view.

"Quiet," said Harry, clutching the side of his temples and willing his brain to remember. "Just give me a minute and I'll get it."

"Could do with it sooner than a minute," said Ginny vacantly from the window.

"Hermione?" asked Ron. "What is it? What's out there?"

Hermione had not looked out of the window very long. Just popped her head out and then back in again, and was now looking at nowhere in particular as she attempted to process what she'd seen. She looked back at Ron, and it was like her face has suffered a fault whilst trying to find an expression appropriate for the situation, and so had instead settled for the blank, factory default one.

"Spaceships," she said plainly. "Lots and lots of spaceships."

Before Ron could even react, Harry cried: "Got it!"

He looked around wildly until he spotted a suit of armour that was still upright just a few feet away. It was dented in places and needed a good polish, but he drew his wand and pressed it right into the chest plate.

"Piertotum locomotor," he said, and the armour's helmet, previously staring straight ahead as if at attention, turned and looked right into Harry. And it wasn't alone; any other suit of armour in the hallway swiveled it's head in Harry's direction, even the ones that had been knocked to the floor twisted their prone bodies to look at Harry. "Hogwarts is threatened," he said to them. "Erm… man the boundaries? Protect us! And err…" he trailed off, failing to remember exactly how Professor McGonagall had put it just before Voldemort stormed Hogwarts, (In fairness, he'd had a lot on his mind at the time), so he settled for: "Look, aliens are here and we think they mean trouble. Don't let them through the doors!"

The suits of armour didn't seem to care about his phrasing, they dropped from their plinths or picked themselves off the floor without another thought and marched off in all directions, drawing swords and raising shields. Hermione ran off too, and as she blew past Harry, he just about heard her mutter: "We'll still need more."

So they ran after her. All four of them sprinted past the mobilising forces of Hogwarts - the suits, the statues, anything capable of mounting a defence - until they were running out of the Entrance Hall doors, and into the darkness.

Except it wasn't quite as dark as when they arrived. Something was illuminating the grounds in front of them - like the force of a thousand moonlights.

"Right," said Ron, finally looking up and seeing what the others had seen. "Spaceships."

What had previously been nothing but giant, glowing orbs (when they were hundred of thousands of miles away), became more detailed now they were only as high as an airplane might be. They were no longer orbs at all. Each of them was a drastically different shape than the other. Cylinders and saucers and shapes beyond description. Some were plated with metal, others looked to be layered with armour like warships and others seemed to be scaly and organic-looking. But they were all firing at each other. Beams of energy and swirling missiles were firing from one craft to the other, and every ship seemed to be at one moment sustaining hits and clouds of flames, and yet attacking whoever else was closest the next.

"What are you doing?" Ron asked Hermione. She was gazing skyward, waving her wand in complicated patterns, and mumbling spells under her breath.

"Protective enchantments," she said. "Like at the battle."

"You think we'll need ones that strong?" said Ginny.

"I'm not sure if there'll even be strong enough."

"I don't mean to out myself as the slow one," said a very agitated Ron, "but could someone catch me up?"

"That noise," said Hermione, still weaving spells through the air as she spoke, "that huge sound that rocked the castle and blew out all the windows – it was a sonic boom. Those things, whatever they are, must have hit the Earth's atmosphere literally seconds ago."

Ron swallowed nervously at his next words. "If something's hitting the atmosphere from the outside, that generally implies they've came from the other direction. As in, not Earth?"

"Yes," said Hermione. Her composure broke, and she turned to look at them with big, sad eyes. "Oh, Harry. You were right. Days ago, when you were sitting on my couch telling us about what you'd seen that night outside your cottage. You said something told you they were extraterrestrial."

Harry didn't have anything else to say. The ships, even whilst fighting one another, still seemed to be descending towards them.

"We might need something stronger," said Ginny quietly, "than suits of armour and protective enchantments."

"Well," said a voice from behind them. "I'm working on that."

There was a brief instinct to turn and look who had spoken, but that was quickly overtaken by the instinct to flinch and grab one's ears, as a horribly high-pitched buzzing cut across the Hogwarts grounds, like someone plugging in an amp. And then that died, and was replaced with music. Strumming guitars, pounding drums, and a beautiful voice singing.

"I can hear music, I can hear music, the sound of the city, baby, seems to disappear…"

"What the hell is that?" Ron yelled, still covering his ears.

And Harry replied with a sentence that was, in context, amongst the most bizarre he'd ever spoke. "I think… I think it's the Beach Boys."

Then they spotted him. Just next to the Entrance Hall was the big blue box, with wires trailing out of the wooden doors, hooked up to an old fashioned gramophone that lay haphazardly on the grass, from which the music of Beach Boys was blasting. And crouched down next to gramophone, sonic screwdriver in hand to amplify the sound, was the Doctor. Tweed, bow tie, floppy fringe and all.

He shrugged at them. "Thought some Beach Boys might calm everyone down. But to be honest," he gazed up at the spaceships, "they do look pretty cross, don't they?"